Very rare freehand protractor 16 for artillery Carl Zeiss Jena in original transport box by Prof. Pulfrich
Using the freehand protractor, it is possible to determine enemy artillery positions.
Such a device can otherwise only be found in the Defense Technology Museum. https://www.wehrtechnikmuseum.de/Exponate/Freihandwinkelmesser/freihandwinkelmesser.html
The specialty of the freehand protractor is that it does not have any optics such as has a telescope. The optics shown influence movements, e.g. in binoculars, the picture. This is what makes the protractor so special.
Here, on the other hand, the targets are just as calm as when looking through a plane-parallel window pane. It is possible to place a battery in the handle. With the help of the built-in magnifying glass, the partial circle illuminated from below with a lamp can be read.
The Zeiss free hand protractor 16 according to Prof. Pulfrich is based on two mirror prisms arranged one behind the other, with the help of which two images can be brought into congruence. The device's battery case is used as a handle and the target is aimed at via the rear semi-permeable prism P3. The line of sight deflected upwards by the prism can, if necessary, be darkened by tinted glasses that can be swiveled in front of it.
At the same time, through the semitransparent mirror S3 in the prism, the sighted auxiliary target is sighted via the second prism system P1 and P2. This is panned until its mirror image coincides with the target. There is also a lever for quick pans and a screw wheel for fine straightening steps.
The partial circle T, which can be illuminated by a lamp at the push of a button, can now be read using the magnifying glass on the top of the device. A vernier scale enables a measurement accuracy of one angular minute. The accuracy is increased by multiple measurements.
Source: Defense Technology Museum
On the left the view and the first (semi-transparent) prism, in front of it a wheel with various darkening discs in the upper and lower view.
At the top right is the reading magnifier, underneath a knurled screw with a lamp holder and the push button for the lamp attached to the transition to the rod-shaped battery container.
On the right is the view for the front pivoting prism. It is pivoted by means of a pivot lever and a fine drive on the left side.
A copy of the operating instructions is enclosed
