The level (from the French. Niveler - “equalize”, “put on a level”) is a geodesic tool for leveling, that is, determining the height difference between several points on the earth's surface. The main method for determining excesses is geometric leveling. To bring the level to the working position, the stand’s lifting screws are used, and the elevation screw is used to accurately level the target axis when taking the count. A straight line between the optical center of the lens and the crosshair of the filament network is called the sighting axis of the telescope. The marking of the levels produced in Russia consists of an alphanumeric code of approximately the following type: 3N2KL. Here, the number 3 denotes the modification of the device, the letter H is the level, the number 2 is the standard error for 1 kilometer of the double stroke in millimeters, K is the presence of a compensator, L is the presence of a horizontal dial for measuring horizontal angles (usually with an accuracy of the order of one degree). Modern optical levels are equipped with an automatic compensator - a device for automatically installing the visual axis of the device in a horizontal (working) position. In levels with a compensator, a cylindrical level parallel to the axis of the telescope may be absent. Most levels also have a round level for rough instrument leveling. All optical levels also have a filament range finder for determining distances along the rail. This is due to the need to control the equality of shoulders when leveling the way "from the middle."