This Carl Zeiss Nivellier III arrived in the collection in September 2017. It was the top model of the series Nivelliers Heinrich Wild had designed during his years at Carl Zeiss Jena. The other two models, the Nivellier I and Nivellier II, were both lesser performing instruments. What they have in common is that they all have the same parts that were patented by Heinrich Wild:

• The anallactic telescope of constant length with internal focusing;
• Device for centring the bubble by making apparent coincidence of its two ends as viewed in a prism;
• Cylindrical steel main axis;
• Dust-tight arrangement for the foot screws.

Over the years the designs that started on these levels made their way to the Carl Zeiss RThII and ThI theodolites.

The Nivellier II is a reversion level, which means that the whole telescope and attached vial can rotate around the telescope axis. In this way any misalignment between them will be cancelled out when observing in two faces (see figure 4 and figure 5).

The 364 millimetres (officially 340mm) long telescope gives an inverted view and has stadia hairs with a 100 times stadia constant.¹ The magnification is 36 times with an aperture of 45 millimetres. Attached to the telescope is the main vial (see figure 1), which is larger than the one on the Nivellier II (see figure 6). Being a reversion level this vial can be turned over to the other side, allowing to eliminate any alignment errors between vial and telescope (see figure 4 and figure 5).

The vial of the Nivellier III has an accuracy of 12" per 2mm run. As the vial is of the coincidence type it should be no problem levelling it with an accuracy of well under 1" or better (0.1mm at 25 metres distance). Optionally a parallel plate micrometer could be fitted to this level, making it as accurate as Wild's later levelling instrument the N3.

With 364 millimetres this level is the largest in my collection.

Based on the serial number (see figure 3) the instrument was made around 1932. The previous owner received the instrument from her father and had no idea about its provenance. From the labels and inventory number "Z.W." (see figure 12, figure 13, and figure 14) it can however be deducted that this instrument once belonged to the survey department of the Dutch government (Meetkundige Dienst van Rijkswaterstaat). Labels at the bottom side of the box indicate that it regularly travelled by train (see figure 15). As can be seen on figure 11 the locking screw of the horizontal drive is signed "Ahrend-6534", a well known re-seller of geodetic instruments, the numerical part being their catalogue entry number.

Despite its age the instrument is in remarkably good state, but sadly incomplete and slightly damaged. The main part missing from the box is the second ocular Nivellier IIIs came with and which was used to reverse the direction one looked through the instrument. For this one had to remove the ocular (see figure 8 and figure 9) and mount the second ocular on the objective end. Of course the parallel plate micrometer is missing, but that was an optional accessory, just like the ones for the Wild NA2 and Zeiss Ni2.

The reflector for casting light onto the main vial is broken, a typical issue most Nivelliers suffer from as its construction was simply designed too light.

Despite this missing ocular and the cracked reflector, the instrument is fully functional and could still be properly used. It came with the original box in which it only fits when the instrument is severed from its tribrach (see figure 12).