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Counting rods
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<p>Counting rods (筭) are small bars, typically 3–14 cm (1" to 6") long, that were used by mathematicians for calculation in ancient <a href="/facts/East_Asia/D8yGVCQX">East Asia</a>. They are placed either horizontally or vertically to represent any <a href="/facts/Integer/PUwwrawx">integer</a> or <a href="/facts/Rational_number/VJQmyY05">rational number</a>. </p><p>The written forms based on them are called rod numerals. They are a true <a href="/facts/Positional_notation/31DECoN4">positional numeral system</a> with <a href="/facts/Numerical_digit/JJdLBoGT">digits</a> for 1–9 and a blank for 0, from the <a href="/facts/Warring_States_period/8P3avwna">Warring states</a> period (circa 475 BCE) to the 16th century. </p>