Tally marks

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A sign warning hikers on the trail to Hanakapiai Beach.

Tally marks are an implementation of the unary numeral system. They are a form of numeral used for counting. They allow updating written intermediate results without erasing or discarding anything written down. However, because of the length of large numbers, tallies are not commonly used for static text.

In Europe and North America, tally marks are most commonly written as groups of five lines. The first four lines are vertical, and every fifth line runs diagonally or horizontally across the previous four vertical lines, in either of the two possible directions (the popular direction may vary from region to region). The resulting mark is known as a five-bar gate, from its similarity to the same. In some variants, the tenth tally is indicated by an X through the previous four rather than just a line. Two groups of five lines (i.e. ten tally marks) are sometimes circled.

Chinese, Korean and Japanese tally marks use the five strokes of 正 which is the character meaning "correct" "proper" and "honesty."

Notched sticks, known as tally sticks also were used for this purpose. The burning of discarded tally sticks resulted in the accidental Burning of Parliament in London in 1834.

To some extent, Roman numerals and Chinese rod numerals are derived from tally marks.