Hatch mark

They are used in three ways as: Hatch marks are frequently used as an abbreviation of some common units of measurement.

In geometry and trigonometry, such marks are used following an elevated circle to indicate degrees, minutes, and seconds — ( ° ) ( ′ ) ( ″ ).

In geometry, hatch marks are used to denote equal measures of angles, arcs, line segments, or other elements.

For example, the numbers I, II, III, V, and X are used, but IV and VI are not used, since a rotation of 180 degrees can make a 4 easily confused with a 6.

The different hatch marks simply signal that the length measurements may (in this case) be considered to be independent of each other.

In the early days of computers, monitors and printers could only make charts using the characters available on a common typewriter.