Architects, designers, builders of roads and communication networks and also people of some other professions constantly face need to count a bias. On the earth's surface it is very difficult to find ideally flat site. The bias is expressed in degrees or as a percentage. Designation in degrees shows a corner of curvature of a surface. But the bias can be presented also in the form of a tangent of this corner increased by 100%.

## It is required to you

- - geodetic compasses or roulette
- - topographic map;
- - level;
- - paper and pencil.

## Instruction

1. The most convenient way to define a bias — leveling. This tool allows to define also distance between the necessary points, and height of everyone in relation to the urovenny Earth's surface. Modern digital levels are equipped with memory devices. For definition of a bias it is necessary only to find between them a difference.

2. The formula for calculation of a bias as a percentage in this case can be presented in the form of simple fraction. The numerator represents it the difference of marks, and a denominator — distance between them. All this is multiplied by 100%. Thus, the formula looks so: % i=Δh/l*100, where Δh — a difference between marks, l – distance, an i – a bias.

3. However there is not always a sense to buy quite difficult and expensive tool. It is necessary to use much more often those means which are on hand. Most often it is necessary to come up against such situations during country works. Choose two points which marks are known to you. They can be designated, for example, on the plan of the site which is formed at breakdown of the territory. Perhaps, near at hand there will be a large-scale map where designations of height also quite often happen. On the site note these points pegs and measure distance between them by means of geodetic compasses. Use the same formula further, as when using of a level. The distance has to be expressed in meters.

4. If you need to determine a bias by the topographic map, attentively look at designations. There it is obligatory to eat horizontals and marks. A horizontal in topography it is accepted to call a trace of crossing of the physical Earth's surface with its-level surface, and all points of any given horizontal have identical absolute value of height. The mark expresses itself numerical value of height of any given point. In the right bottom corner of the topographic map there is always a schedule of laying by which it is possible to determine a tilt angle very quickly.

5. During the work with the topographic map consider several moments. A mark of a point find on the next to it horizontals. If the point is on the line, then the numerical value of its mark precisely coincides with the specified value. The interpolating method is applied to the points which are between horizontals. In the simplest cases there is just average value. Calculate distance on scale. Find a ratio of a difference of marks and distance between points and increase fraction by 100%.