The topographic level, also called optical level, engineer's level or equialtimeter, is an instrument whose purpose is to measure differences in level between points that are at different heights or to transfer elevations from a known point to an unknown point.

They can be manual or automatic, depending on whether the main level must be calibrated horizontally at each reading or whether this is done automatically when the instrument is placed "in station".

The optical level consists of a telescope similar to that of the theodolite with a stadimetric reticle "Reticle (piece)"), for aiming and a very sensitive bubble level "Level (instrument)") (or a gravity or magnetic compensator in the case of automatic levels), which allows maintaining the horizontality of the optical axis of the telescope, both are jointly joined so that when the level is unlevel, the axis of the telescope does not maintain perfect horizontality, but leveling the level also horizontalizes the optical axis.

In the last thirty years there has been such a change in these instruments that at that time, in the early 1980s, almost all the instruments used were of the manual type, but at this time it is rare to find one of those instruments, even the brands that still manufacture them are rare, since the manufacturing techniques have been perfected so much that the automatic ones are as precise and reliable as the manual ones, despite the mistrust that the first models aroused in the old surveyors. automatic.

This instrument must have special technical characteristics to be able to perform its function, such as a bubble to be able to level the instrument, a telescope with sufficient magnification to be able to see the divisions of the sight, and a reticle "Reticle (piece)") with threads to be able to aim and take readings, as well as the possibility of a compensator to ensure its perfect leveling and horizontality&action=edit&redlink=1 "Horizontality (plan) (not yet written)") of the plan of comparison.

The optical level consists of several essential parts:

The accuracy of a level depends on the type of leveling for which it is used. The normal thing is a level of between 20 and 25x magnification and centimeter or double millimeter sights. With this level and the appropriate methodology, leveling can be done with an error of approximately 1.5 cm per kilometer of leveling.

For more demanding jobs, there are levels with split bubble level, wedge reticle, flat-parallel plates with micrometer "Micrometer (instrument)") and millimeter INVAR sights), with which precisions of about 7 mm per kilometer of leveling can be achieved, with the appropriate methodology.[2]​[3]​[1]​.