Hatch mark

Hatch marks (also called hash marks or tick marks) are a form of mathematical notation. They are used in three ways:

Hatch marks are frequently used as an abbreviation of some common units of measurement. In regard to distance, a single hatch mark indicates feet, and two hash marks indicate inches. In regard to time, a single hatch mark indicates minutes, and two hatch marks indicate seconds. In geometry and trigonometry, such marks are used following an elevated circle to indicate degrees, minutes, and seconds — ( ° ) ( ′ ) ( ″ ).

Hatch marks can probably be traced to hatching in art works, where the pattern of the hatch marks represents a unique tone or hue. Different patterns indicate different tones.

Unit-and-value hatch marks are short vertical line segments which mark distances. They are seen on rulers and number lines. The marks are parallel to each other and are evenly spaced.

The distance between adjacent marks is one unit. Longer line segments are used for integers and natural numbers. Shorter line segments are used for fractions.

Hatch marks provide a visual clue as to the value of specific points on the number line, even if some hatch marks are not labeled with a number.

Hatch marks are typically seen in number theory and geometry.

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

Hatch marks for congruency notation are in the style of tally marks or of Roman numerals – with some qualifications. These marks are without serifs, and some patterns are not used. 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.

For example, if two triangles are drawn, the first pair of congruent sides can be marked with a single hatch mark on each. The second pair of congruent sides can be marked with two hatch marks each. The patterns are not alike: one pair uses one mark while the other pair uses two marks (Figure 1). This use of pattern makes it clear which sides are the same length even if the sides cannot be measured. If the sides do not appear to be congruent, as long as hatch marks are present and are the same number of hatch marks then the sides are congruent.

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Wikipedia