Prismatic compass

A prismatic compass is a tool used in navigation and surveying to help find directions and measure angles. It is very useful for figuring out the direction of lines and points during surveys. This kind of compass helps determine the direction of lines by using a magnetic needle, and the actual distance between points can be measured with a tape, chain, or a laser range finder.

The prismatic compass gets its name from the special prism it uses, which helps make observations more accurate. Surveyors often use it to create lines called traverses. They take two directions, called fore bearing and back bearing, for each line, and these should differ by exactly 180^° if there are no special local effects on the compass, known as local attraction. This tool is important for making sure surveys are precise and correct.

Least count

Least count means the smallest amount an instrument can show. For a prismatic compass, this is 30 minutes. This means the compass can only show angles that are multiples of 30 minutes, like 5° 30', 16° 00', or 35° 30'.

Bearings

A compass helps find directions by measuring angles in a special way. It uses a system called the whole circle bearing, which measures angles from 0 to 360 degrees clockwise from magnetic north. This helps figure out the angles between different paths during a survey. There are simple rules to find these angles, depending on the direction of the path.