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Structure of mechanism |
| Function |
This instrument is housed in a wooden case. There is a plumb line in one of its compartments. The device consists of three parts to be assembled: the telescope, the spirit level and the base. The telescope in mounted on the base via two brackets closed by a clasp. It consists of an object lens, an eyepiece and a rack and pinion screw which is used to focus the image. A screw located below the telescope enables
It to pivot in the vertical plane to adjust its horizontality.
On the telescope there is a spirit level in a brass tube. The base comprises a stand with a plate at the bottom, which can turn with respect to 3 blocking screws. One screw is used to block the rotation of the stand, and thus the complete unit, but this screw is damaged.
This device is used in topography to measure the altitude of a point by reading two points on a target. These measurements are later used for building construction or the elaboration of plans. The builder’s level is screwed to a tripod.
The target is a graduated vertical rule, generally 4 metres high. The first step is to set the device horizontally via the footscrews and spirit level. The second step is the sighting itself.
The altitude of a first point, A, is considered as known. The height of A is read by sighting the level on the target positioned at A (a manoeuvre known as the backsight). The target is moved to point B, whose altitude is unknown. Another reading is made (the foresight). The altitude of B is equal to the altitude of A added to the difference (plus or minus) between reading A and reading B (altB = [altA +(reading A- reading B)]). The level can also be used to adjust the height of an element if its reference level is known. |
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Guidance function |
| Trace of a dedicated point on follower |
 Open trace |
| Dimension of mechanism |
spatial |
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