Welcome to the web site of Nicolàs de HilsterI am a hydrographic surveyor by education and the founding owner of a company in specialised measurements in the hydrographic and geodetic field. Main field of work are offset surveys and calibrations of hydrographic survey, offshore and naval vessels, and lecturing at the bachelor hydrography course at the Maritime Institute Willem Barentsz on the isle of Terschelling, the Netherlands.
In my private life I am a collector and independent researcher of nautical and geodetic instruments. The main focus of my research lies on instruments used for latitude determination at sea from Thomas Harriot to John Hadley and their contemporaries. Part of my research is creating reconstructions and replicas of the instruments and to use them in the field for a better understanding of their capabilities. In addition to that I am interested in geodetic instruments and their development from Martin Waldseemüller to Heinrich Wild and their contemporaries.
This web site gives an overview of a part of my collection of nautical and geodetic instruments and the research on them, the works I consulted and collected on the topic and papers I published. The current page is my slowly but surely growing blog.
June 2016This month I was hinted that a variable Fall or Rise 'slope' attachment for the Cowley level was available on an on-line auction. This simple attachment allows the Cowley level to be used to set out slopes with gradients up to about 1:10 (see figure 21).
March 2016This month the third model of Wild's first levelling instrument entered the collection. The 1970 Wild NK2 is the modern styled version of the 1951 Wild N2 in the collection. The addition K in the model name also indicates that this instrument is equipped with a horizontal circle, in this case centesimally divided, an option Wild introduced in 1924 with its Wild NKII.
February 2016This month a Cowley level was donated to my collection. This very simple instrument, invented in 1944, looks like an old fashioned amateur camera than a levelling instrument and was one of the first popular automatic levels that was produced.
September 2015This Wild T2 theodolite, also known as the Wild T2 mod, arrived in the collection this month. It was formerly owned by the Maritime Institute Willem Barentsz (MIWB) on Terschelling, where it has been used from 2002 until 2014 for teaching purposes (see adjacent picture), mainly for sun azimuth observations using a Roelofs prism. At the start of the new academic year 2015-2016 it was replaced by a more modern Leica TCRA1101 from 2001, which also is used for the same observations.
June 2015This month a Kern DKM2 theodolite entered the collection. It came from the inventory of the Hogeschool Utrecht where it was used for educational purposes, but since this month it is on long term loan in my collection.
When Heinrich Wild left Wild Heerbrugg he joined Kern Aarau where he continued designing theodolites. The Kern DKM2 was meant to be the competitor of the Wild T2 and thus has similar specifications. The DKM2 shows features well known from Wild's original designs while working in Heerbrugg, but at the same time this instrument shows that his ideas kept on evolving while working at Kern in Aarau.
May 2015This month I finally managed to find myself an early AGA Geodimeter 112 for the 1980 SAT AGA-Minilir. Originally the Minilirs were bought with AGA 112 EDMs, but those were discarded in 1998 and replaced by Ibeo Fennel EDMs. The one shown here is only a few dozen serial numbers away from the first AGA 112 that was bought for the Minilir.
April 2015Last December this level came up for auction on a Dutch on-line auction site. Being in a terrible state little enthusiasm was displayed by potential buyers for this early Carl Zeiss Nivellier I. After more than four months waiting for a higher bid, the seller decided to agree with the offer I made. It took some 10 hours of careful cleaning to present it in the current state.
Februari 2015This month a levelling instrument by Wild Heerbrugg, the Wild N1, came up for sale on a Dutch on-line auction site. Here in the Netherlands it was dubbed "Baby Wild" as it was the little brother of Wild's standard levelling instrument, the Wild NII.
Januari 2015This month two Geodimeter System 400 total stations were donated to the collection by a former teacher of the Internationale Agrarische Hogeschool (International Agricultural University) Larenstein.
According to the manufacturer the Geodimeter System 400 was the first surveying system where hardware and software were integrated in an intelligent and powerful unit.
September 2014Last month another instrument entered the collection, but only made it to my web site this month. This time it is a 1948 Wild T1 complete with original metal dome and wooden transportation box. The Wild T1 was the predecessor of the Wild T1A that was already in the collection.
August 2014This month I found this rare piece of geodetic history: a 1943 CT&S Tavistock. It came up for sale on an on-line auction site, but having quite a few broken and bent parts not too many people were interested in it. To me it was a nice opportunity to see how easy it would be to get it up and running again. Some eight hours work turned this derelict instrument back into working order again...
July 2014This month a Wild Heerbrugg RDS came up for auction on a Dutch auction site. The abbreviation RDS stands for Reduktions Distanzmesser für Senkrechte Latte or 'Reduction Distance-meter for a Vertical Staff'. The RDS is one of the rarer theodolites Wild produced. It was a successful attempt to create a self reading tachymeter that would not simply give the slope distance to the assistant holding the vertical reference staff, but the horizontally reduced distance and the height difference.
June 2014Although in my collection since 2012, I did not find the time yet to add the 1992 Krupp Atlas PolarTrack to my web site. The PolarTrack was the relatively cheap successor of the Fennel/Minilir and partially came from the same manufacturer IBEO.
After acquiring the original tripod in 2013 I now finally found some time to photograph the instrument and create the story around it.
May 2014Only a few days old this month added 37 inches to the collection with the acquisition of two standards: a Standard Inch and a Standard Yard. Both were made by William & Thomas Avery, Birmingham, and date from 1875 (the Yard) and late 19th century (the Inch). They form a perfect combination with the other standard in de collection: the Doyle & Son 66ft Standard Chain.
Last year I was donated a Breithaupt PRURO circle testing collimator. It has taken a while to create its stand, but now it finally made it to my web site.
April 2014This month I visited the impressive Louwman Collection of Historic Telescopes of befriended collector Peter Louwman in The Hague. The collection was only recently made accessible to the public in the Louwman Museum, home to the world’s oldest private collection of motor cars which was compiled by two generations of the Louwman family. In the museum the Louwman Collection of Historic Telescopes found its own place. Next year the Scientific Instrument Society is planning a study tour incorporating the collection and being the SIS representative for the Netherlands Peter and I met to make initial arrangements.
After more than a year this month the new design of my own web site is finally launched. Most instruments have been re-photographed, showing them with much higher detail than before. All accompanying stories have been checked and partially re-written. Finally several instruments have been added and a search function implemented. Now the site shows instruments from the end of the 16th century up to the very end of the 20th century. Enjoy watching and reading!
Those who are eager to know what has changed since I stopped maintaining the old site have to go back to August 2012.
February 2014At the end of the 20th century the first robotic total stations saw the light. The advantages of the AGA/Minilir and Polartrack had not stayed unnoticed and thus the demand for robotic instruments increased and lead to new developments in geodetic instruments.
By the middle of the 1990s the best instrument money could buy was the Leica TCRA1101. I bought one for fieldwork in 2008 and another one in 2012. Still today the instrument is a fine piece of equipment to work with and therefore it still is in continual use. Having already several total stations on this site, this month I thought it would be appropriate to add the TCRA1101 to it.
January 2014In 2010 I was contacted by a client to do a job for him. We soon found out that our professions brought us a mutual hobby: collecting geodetic instruments. When the job was done he was that satisfied that he decided to donate a 1960s military Wild Heerbrugg T2 with an Autonetics ABLE gyro attached to it to the collection.
It took me several years to find out what exactly it was he had donated. Thanks to the increasing amount of documents coming available on the internet (possibly because of declassification), I finally found out what the original set was consisting of and what it was used for. This month I have written an article on the T2-ABLE combination and placed it in the geodetic section.
October 2013When Heinrich Wild started his own business, the first instrument he produced was the Wild NII in 1923, the forerunner of the N2. A year later he added a horizontal circle to the NII. Although in later years this would mean the model name would be extended with a K (for Kreis, German for circle), in 1924 this was still named NII (but I will use NKII for clarity).
This month a Wild NKII with the extreme low serial number 960 was found during a house clearing in the Amsterdam area and almost ended up in the skip. Luckily they thought of putting it on a Dutch auction site and that is how it ended up in the collection.
May 2013A few years ago I managed to add a Wild Heerbrugg T3 to the collection. That was an old sexagesimal one from 1937 with an astronomical reticle. Here in the Netherlands we are used to work with centesimally divided instruments, so I was still looking for an opportunity to lay my hands on one. Centesimal divided T3s are however almost as rare as rocking horse manure, so I had to be patient. This month finally a centesimal Wild T3 came up for sale. Not only was it centesimally divided, but it also was from 1939, two years before Heinrich Wild introduced the T4.
February 2013Every now and then really rare instruments show up on auction sites. This time it was an 1924 Carl Zeiss Nivellier II levelling instrument. This is one of the models Heinrich Wild created during his years at Carl Zeiss. The instrument came with a remarkable complete box and although it had to come all the way from Latvia, it arrived safely at the collection a few weeks later.
November 2012In the 19th century levels were mostly made of lacquered brass. In the collection there already was an Egault type level by Secrétan à Paris and this month I have added a Lenoir type level made by Tibaut Desimpelaere in Brussels to it. Both levels are quite basic and not of the best design. Having loose telescopes without a fixed vial makes them susceptible to errors as dirt could easily end up between the surfaces of the frame, telescope and vial. Still these levels have played an important role in geodetic history and are therefore worthwhile mentioning and collecting.
October 2012Recently I bought a new (second hand) Leica TCRA1101 Plus total station and in the same deal acquired a Wild Heerbrugg T1A for the collection. The T1A was Wild's first automatic theodolite, which means that the vertical circle is set vertical automatically.
September 2012This month a rare Wild instrument came up for auction for a very reasonable price. Having worked with it myself on a tropical pipeline project, the temptation was simply too large and I decided it had to be added to the collection. The instrument, the Wild Heerbrugg T0, was Heinrich Wild's answer to the American transit.
August 2012Last year we had a new house built, which meant that the collection was put into temporary storage for considerable time. After it was 'recovered' and placed into our new library I decided that it was about time to overhaul my web site as well. Most pictures were out of date, while the lay-out could do with a refreshment as well.
Designing started in winter 2013, while the actual work on it started on it in May 2013 and lasted until April 2014. During that period a whole new lay-out was made using the well known colours and most images have been re-taken.
In the meanwhile the old site was no longer updated, even though the collection kept on growing. New acquired and several, formerly not exhibited, existing items found their way onto the web. The blog is still here and I have updated it in this new lay-out ever since. Enjoy reading!
July 2012This month an instrument of legendary proportions (at least here in the Netherlands) was donated to my collection. This instrument, the 1980 SAT AGA-Minilir was the first autotracking total station and has been used to position vessels at, and piers of, the Eastern Scheldt Storm Surge Barrier during its construction in the 1980s. The instrument was initially combined with a Geodimeter AGA 112 electronic distance meter (EDM), which was later replaced by the IBEO Fennel PS 50 EDM. Depending on the EDM used the system became known as either the AGA/Minilir or Fennel/Minilir.
May 2012After having found Heinrich Wild's first two theodolites he designed for (or had design features by him) for Carl Zeiss, the 1924 Zeiss Th1 and 1926 Zeiss RThII, it was now time to get Wild's first own theodolite, the Archetype Wild T2. A befriended collector kindly pointed me to it when this one became available on an on-line auction site and this is how the instrument ended up in the collection.
April 2012Recently we have moved to a temporary home causing some silence on my blog. Last April I was informed that a 19th century 66ft standard chain came up for sale on an auction site. Having two 'normal' chains in my collection; the 19th c. Lerebours chain and the 20th c. Chesterman chain made me decide to add this rarity to it. It came in a box and is invested with hallmarks as can be seen on adjacent picture.
October 2011As may have been noticed I have switched off my weather cam some months ago. Instead I wanted to use that area on my web site for an other set of instruments and tools I have in my collection. Under the header Tools I will add steel tapes, chains, clinometers and other tools used in surveying. The first to be added are an early 20th c. Tibaut steel tape, a mid 19th c. Lerebours chain (see adjacent picture), and an early 20th c. Chesterman chain.
September 2011Strange how things can go when one uses and collects older instruments. It was only last May when I found a famous theodolite designed by Heinrich Wild during his years as manager of the Geo department of Carl Zeiss, the 1924 Zeiss Th1. Now I laid my hands on a 1926 Zeiss RThII, the first theodolite to feature Heinrich Wild's patents. This one once belonged to J.Th. Wouters, a Dutch architect.
August 2011A few weeks after I bought a 1961 Wild N3 for a product development within my company, a client who heard about it decided to donate this newer version, the 1977 Wild N3 to my collection. Judging from the impeccable state it is in, the instrument has spent little time in the field. The instrument was the latest version of the Wild N3 and design-wise it is very similar to the Wild TC1 Total Station in my collection which also dates from the same period.
July 2011For a new product development of my company I needed two Wild Heerbrugg N3 levels. A geodetic instrument dealer here in the Netherlands had two them in stock; one from about 1962 (serial 106547) and this one from 1961. Despite being the oldest of the two the 1961 Wild N3 is in an amazing brand new condition, due to the fact that it has only been used for educational and research purposes at the Delft University.
May 2011This month I was at the workshop of a Leica dealer here in the Netherlands in an attempt to get the 1980 Wild TC1 repaired. Although sadly enough the repair has failed, the discussions about early geodetic instruments lead to the discovery of a 1924 Zeiss Th1 optical theodolite on E-bay. This particular instrument was the first theodolite that combined glass circles with an optical plan parallel coincidence reading mechanism and marked the dawn of a new era in theodolite design and influence later models like the Wild T2 and Wild T3. After a few days of negotiations the instrument finally ended up in my collection.
April 2011I have added a new instrument to my collection. This time I obtained a Pantometer through an auction web site. The instrument combines the functions of an Equerre with those of a Graphometer or Pseudo Holland Circle. Having 'worked' in Argentina the instrument has seen more of the world that I did...
March 2011Recently a collector came to me with the request to restore an early Davis Quadrant. The instrument was bought without any vanes, but in style it was remarkably similar to the replica of the 1734 Davis quadrant I made (which is a replica of of an original in the National Maritime Museum in Greenwich). The restored Davis Quadrant has a declination scale with English inscriptions and based on a Julian calendar, which indicates it was made before 2 September 1752 (the date the British turned to the Julian calendar). Using original woods and ageing techniques all four vanes were recreated in the style of the instrument (see pictures 19 - 21 for the fully restored Davis Quadrant).
December 2010I found this 18th century Surveyor's Cross while scouring the internet for antiques dealers. The instrument is a simplified form of the Holland Circle (Hollandse cirkel). Compared to it the instrument lacks a compass, the suspension ring for vertical measurements, and it has been engraved in degrees only. Holland Circles also had trigonometrical scales (sine, tangent and secant) and sometimes a Polygon scale similar to the one on the 17th C. Surveyor's Cross in my collection. Due to its simplified form the instrument is sometimes referred to as a Pseudo Holland Circle.
October 2010From 9 October 2010 until 6 February 2011 the maritime museum in Vlissingen, muZEEum, features the exhibition Geheime Kaarten in Zeeland, Getekend voor de VOC (Secret Maps in Zeeland, drawn by the VOC). The exhibit shows maps and instruments made and used by the Zeeland Chamber of the VOC. Being mainly used by Zeeland chamber of the VOC one of my reconstructions of the spiegelboog will be part of the exhibition. The spiegelboog - invented in 1660 by Joost van Breen, the later examiner of the mates of the Zeeland chamber of the VOC - was the first reflecting navigational instrument (picture at the right by Esther Boogaard).
September 2010With a generous donation by my family for my birthday I could make this long lasting wish come true; adding a 1939 Wild T3 (geodetic) to my collection (at the right on the picture). A search on the internet initially resulted in two instruments in the US, but both were incomplete. Finally I found myself this complete early one.
In addition to that I am trying to get all levels in my collection on-line as well. The first of them is the 1951 Wild N2 (at the left on the picture). It came into my collection as part of a generous donation by a former colleague in 2008. Up to now I lacked the time to get all instruments from that donation on-line, trying to get it done now though...
June 2010This month my article on the 1618 Demi-cross reconstruction was published in bulletin 105 of the Scientific Instrument Society. The article is available as download from the demi-cross page.
May 2010In 2006 I met clockmaker Günther Oestmann of Ars Mechanica at the National Maritime Museum in Greenwich. He then had a talk on casting an astrolabe, which he had recently done. After the talk we discussed the possibility to create a copy of the 1580s Mariner's astrolabe for my collection. I created an AutoCAD drawing based on the dimensions of an 1588 original, which Günther used to have the body cast. This month we met again during the A Sense Of Direction symposium and I was presented the astrolabe which he had made. On the adjacent picture Günther, who stands on the right, hands over the astrolabe to me.
On the conference I presented a paper on the early development of the 1734 Davis quadrant, which will be published later.
November 2009The National Museums of Scotland invited me to display my collection of replicas and reconstructions of early Celestial Navigation instruments at the launch of the 350th anniversary of the Royal Society, held in the National Museum of Scotland on 30 November, 2009. The image shows my instruments next to the replicas the museum was able to commission thanks to funding by The Royal Society.
The inset shows a full view of the table with from left to right: 1590 Hood's cross-staff, 1661 Kronan cross-staff, 1660 spiegelboog, instruments for electrical experiments, 1618 Demi-cross, a weather glass, telescope and lodestone, 1623 hoekboog, a globe, 1734 Davis quadrant, a magic lantern and 1720 Hasebroek cross-staff.
October 2009Although still available from C. Plath, the price was that high - about half their top model sextant - that I decided to recreate the pentagon prism attachment that once belonged to my 1956 geodetic sextant. I have spent quite a few enjoyable hours in my garage, cutting, drilling and heating some brass, the result of which can be seen here. Together with the pentagon prism attachment I made a new adjustment tool that is long enough to get beyond it and all for just little over the additional costs of their mahogany cases.
September 2009A friend of mine tipped me off that a 17th C. Surveyor's Cross was for sale on a Dutch auction site. After a week of bidding it finally came into my hands at a very decent price. When I collected it (some 200 kilometres away from here, close to were this friend lives) my friend asked me whether I would appreciate a 1980 Wild TC1 as well as a donation to my collection. Of course this was an offer to good to be true, so the collection has grown with another two land survey instruments.In addition to that I cleaned the 1956 geodetic sextant by C. Plath that I already had in my possession since last year. As the instrument was extremely corroded it took a mere five hours to get it a bit neat again.
August 2009Almost a year after I obtained the Keuffel & Esser transit I finally had time to repair the missing wire from its reticle. The reticle of this instrument was made of spiders cobweb of which only the horizontal stadia wires survived. The picture at the right shows the cross-orbweaver that kindly donated one of his threads through the repaired telescope of the transit. Repairing the cross-hair of the reticle took about three hours. See figures 15 to 20 on the 1919 K&E page on how this was done.
July 2009After four years of research I finally made a reconstruction of yet another early navigational instrument: the 1623 hoekboog (double triangle). It was developed in the early 17th century, around the same time as the 1618 Demi-cross and mainly used by Dutch navigators.
June 2009During (or rather at the end of) the 2009 SIS conference in Paris, France I visited this flea market where I found this old box with interesting content. Not only did it contain an equerre, but also a 19th c. Secrétan Egault level. The level was remarkably complete and in very good condition.
In addition to that this month my article on the 1590 Hood's cross-staff reconstruction was published in SIS Bulletin 101.
May 2009Another superb donation to my collection in 2009 next to the donation of the 1984 Kern E1. Being a left-over in an inventory, the previous owner had little use for this Leica NA2 with Wild GPM3 parallel plate micrometer and decided it would fit better in my collection than on the market. This level was originally developed by Wild Heerbrugg and was one of best they ever made with only the Wild N3 being more accurate.
April 2009I have added three theodolites to the land survey section which I received from (or swapped with) former colleagues last year; a 1962 Wild T2, an Askania Tu 400 and an early Carl Zeiss Th42 (the latter has left the collection in 2011). These instruments have an angular resolution of 0.0002gon, 0.001gon and 0.01gon respectively, so quite different instruments for different purposes. Although I am not sure about the manufacturing years of the last two instruments it seems in this case that by coincidence the accuracy is disproportionate with the manufacturing year (so the older, the better).
February 2009A colleague donated this instrument to my collection, for which I am very grateful. The instrument is a 1984 Kern E1, one of the first total stations made. It has served many years in the field and now finally retires in my collection while still in perfect working order.
November 2008A test bid on the internet accidentally resulted in this 1919 Keuffel & Esser Preliminary Survey Transit (model 5129N). I was only one dollar above the reserve (which was very reasonable) and nobody was feeling like overbidding me (perhaps because of the world wide financial crisis?). Never mind, I am happy with this new addition!
October 2008Through a Dutch auction site I found myself these two bottles. Together they form a level instrument for hydrostatic levelling. Once bought by Corus for shaft alignment, they were discarded some 20 years ago and subsequently taken home by one of their employees.
September 2008Another Ebay item: Again after searching for it for several years I finally got myself a 19th c. water bottle level. This is as basic as it can be; two communicating bottles of water, attached to each other by a brass tube.
July 2008A lucky bid on Ebay: After searching for it for several years I finally got myself a Roelofs Solar prism for my Wild T2. Although of Dutch origin, this one came all the way from Fairbanks, Alaska. The Roelofs Prism can be used for sun shots, which in itself are used to determine true north in the field. In my case I use the Roelofs Prism for gyro calibrations. Using a simple spreadsheet on my mobile phone I get accuracies of about 0.005 degrees, which is more than enough for a proper calibration as the gyros that I calibrate (Fibre Optic Gyro's or FOG's) have an accuracy of about 0.3 degrees.
May 2008The annual study conference of the Scientific Instrument Society was held in The Netherlands from 6th until 9th May, 2008. They not only visited several museums, but also had the chance to see the work of Tatjana van Vark in Ede and my instruments and dividing methods in Utrecht at the Utrecht University Museum (Picture by Otto van Poelje, Chair of the Oughtred Society Award, The Netherlands).
March 2008Last year I was commissioned to create a set of early 17th century navigational instruments for a new museum in Hirado, Japan. The set consisted of a demi-cross, a cross-staff modelled after the one found on board of the Kronan, a traverse board and a chip log with hour glass.
November 2007Another reconstruction finished: Master Hood's cross-staff from 1590, the start of a new development in navigational instruments.
This instrument has been described in period literature during the period 1590 - 1622 and was used for shadow observations of the sun in a forward manner and for land surveying.
October 2007It is finally finished: the reconstruction of a 1618 Demi-cross, an early Dutch backstaff after an instrument by Captain John Davis.
This instrument has been described in period literature during the period 1618 - 1693 and was used for backward observations of the sun.
September 2007After a long period of no updates on my web site I finally have some news. To start with I found myself a new object: a Cotton Type Range Finder.
This instrument was used some one hundred years ago to measure distance to objects at sea that have known dimensions.
The other news is that since November last year I have been researching the development of the Davis Quadrant. During this research I stumbled upon blue-print like sketches of an instrument from 1618 called the Demi-Cross. With the reconstruction of it nearing it's completion I will soon upload a page on this instrument.
November 2006At the 2006 Navigational instruments as a source of historic information symposium at the National Maritime Museum in Greenwich I presented the spiegelboog (Mirror-staff in English) to an interested audience.
On this picture by Jeremey Spencer I am explaining the instrument to Wouter Heijveld (Curator of Navigational Instruments Rotterdam Maritime Museum), Gloria Clifton (Head of Royal Observatory, Greenwich) and Richard Dunn (Curator of History of Navigation, National Maritime Museum, Greenwich).
September 2006Finally after two years of research a complete article on the spiegelboog (Mirror-staff in English) was published in the Bulletin of the Scientific Instruments Society.
The Scientific Instrument Society (SIS) was formed in April 1983 to bring together people with a specialist interest in scientific instruments, ranging from precious antiques to electronic devices only recently out of production.
The Society has a truly international membership offering those who join the chance to link up with instrument devotees across the world.
August 2006My latest find: a brass octant by T.S. & J.D. Negus, New York.
In January 2007 I have been in contact with the great great granddaughter of John Davidson Negus. Much of the details on the Negus page originates from her research.
January 2006Delivered two cross-staffs to museums: one ebony cross-staff at the Archenhold Observatorium in Berlin, Germany and the copy of the Kronan cross-staff to the Kalmar Läns Museum in Kalmar, Sweden.
November 2005My latest project is finished: creating a copy of the Kronan cross-staff. In the meanwhile I'm starting research on another long gone navigational instrument: the Dutch version of the Davis quadrant: the 1623 hoekboog.
October 2005On the 22nd of October 2005 I presented a paper on the reconstruction of the spiegelboog at the 'Who needs scientific instruments?' conference at museum Boerhaave in Leiden, The Netherlands.
On the 11th we did a field test with my replicas.
September 2005My latest find: an 1943 U.S. Navy stadimeter. This instrument was used to measure the distance to ships at sea and is based on a sextant.
May 2005Combined my holiday with a visit to the Kalmar Läns Museum where I met Lars Einarsson and Max Jahrehorn. They allowed me to measure the 1661 Kronan cross-staff which I will build later this year.
April 2005A project is finished: The reconstruction of a spiegelboog (Mirror-staff in English), an instrument by Joost van Breen.
If you have any questions and/or remarks please let me know.