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Fully Functional Antique Theodolite

A Theodolite is an instrument for high precision angle measurements used at many scientific fields, such as: Astronomy, Archaeology, Geodesy, Cartography, Architecture…

With a Theodolite it is possible to measure horizontal and vertical angles between objects from great distances. Measuring the right angles can give us enough information to determine our own position, calculate the coordinates of any point that is visible through the telescope, or finding the north direction in an already existing coordinate system.

This Lego theodolite model contains all the instrument parts and setting options that are required to do the exact same measurements – except of the printed (or engraved) lines marking the angles on the two circles.
Still, it illustrates all working mechanisms of these old instruments, and it can be an excellent visualisation tool, or office/home decoration.

The first theodolites were made by watchmakers in the early XVIII century. Modern versions are still in use for engineering purposes, but they are far less attractive than their ancestors.

1. Gravitational level / Tubular level
This part indicates the tilting of the instrument. It works very similar to a spirit level (or bubble level) which can be found on real-life theodolites, but this solution is much simpler and can be built out of Lego parts.
When the small red cylinder is exactly in the middle that means the base of the level is horizontal along it’s length. (It can be still tilted in the perpendicular direction, this is why the level is always attached to the rotatable frame, so the operator can check the tilting from every direction.)

2. Levelling Screws
There are three screws around the base that are meant to change the height on each side.
With adjusting these levelling screws, it is possible to set the instrument in a perfectly horizontal position. 

3. Horizontal and Vertical Fine Motion Screws
With the fine motion screws or “micrometer screws” we can turn the telescope very slowly and very accurately.
The fine motion screws are not connected to the horizontal and vertical circles in a permanent way, so the gears can be mechanically separated. This lets the telescope turn freely for a faster realignment. When the telescope is pointed roughly to the right direction, the fine motion screws can be applied again for precise movement.

4. Optics
Every telescope should have at least one eye lens (ocular) and one object lens (objective).
The objective has to be less curved, and their focus points have to meet to get a sharp image. 
The only lens piece Lego ever made is the minifigure magnifier glass, which has a standard curve and a very short focus. In the absence of various lenses, the focal setting mechanism is still functional, but the telescope will not be able to produce a sharp image.

5. Plummet
The plummet was a very simple, but essential accessory for ancient theodolites. When the instrument had to be set up above a geodetic control point (a permanently marked point with known coordinates), the operator attached the string of the plummet under the centre point of the Theodolite.
The tip of the plummet showed exactly what was under the centre point, so the operator could slide the baseplate into position.
This could be a rather unpleasant task in strong wind...

For more information on theodolites please visit:

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