Bobby Pacho

Also called glasses/level, the optical level is used to make levellings. It is composed of optical glasses fixed on a tripod. It is used by the operator to read measurements on a scale (test card), which is held by an operator.

One distinguishes various types of level, and in particular:

level with double aiming, in which the bubble and possibly the glasses can give two opinions, which makes it possible to carry out two aimings. Even when the level is not regulated, the average of the readings is correct, compensating for the field alignment error by double reversal.
level with Sight S, with a bubble associated with a rule carrying the Azimuth reading device.
level of Égault, comprising a toric bubble interdependent of the main axis and two clamps, on which puts back a removable sight tube. The unit can turn of 200 gon S around the main axis to carry out a second aiming.
the levels used usually are known as “automatic levels”, because after a setting with the horizontal rapid and coarse by the operator, the axis of aiming is put automatically at the perpendicular of the vertical of the place.
the levels of last generation are known as “electronic” or “with code bars”. The test card is provided with code-bars, that the level decodes. The reading, the recording, posting and the transfer on computer are automatic.

Certain automatic levels can be equipped with a “blade micrometer” “with parallel faces”, and are then used jointly with Mire S in Invar for levelling S of precision.

The levels are used mainly by:

the geometrician S
the topographer S
actors of the economic sector of construction
work-public the

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