Put the compass spike at the bottom of the circle and draw an arc that touches the top of the circle and extends more than half way down each side... Image caption, ...then keeping the compass ...

Sundial and compass with perpetual calendar and lunar circles. Brass, part silvered, 6 1/8 x 5 3/8-inches. By Christopher Kohler, Dresden, Germany, 1677. Glass of compass box cracked, compass needle ...