Editing Opisometer (section)

== Explanation ==
A simple opisometer consists of a toothed wheel of known [[circumference]] on a handle. The wheel is placed in contact with the curved line to be measured and run along its length. By counting the number of teeth passing a mark on the handle while this is done, the length of the line can be ascertained:

:line length = wheel circumference &times; teeth counted/teeth on wheel.
<!--If TeX must be used, one should write \mathrm{line}\ \mathrm{length}, etc.
:<math>line length = wheel diameter \times teeth counted / teeth on wheel</math> -->

In more sophisticated models, sometimes called a '''chartometer''', the wheel is connected via gearing to a rotary dial from which the line length can be directly read.<ref>[https://books.google.com/books?id=ThXH7xmUskIC&dq=opisometer&pg=PA83 Gerard L'Estrange Turner, ''Scientific Instruments, 1500-1900: An Introduction''], Philip Wilson Publishers 1998, {{ISBN|0-85667-491-5}} (p.83)
</ref>

The instrument is most commonly used to measure the lengths of roads, rivers and other line features on [[map]]s.  Opisometers designed for this purpose provide scales reading the measured distance in kilometers and miles.