Semi-circle-Brass 2.75" (7cm) radius. Graduated on face 0-180 with signs of zodiac. 0-180. Three scales of months of the year and days in month. On back of semi-circle are 14 scales marked with signs of the zodiac and graduated 12-8-12, 1-4-1, 7-12-7, 5-0-5, 12-7-12, 1-5-1, 7-12-5, 12-8-12, 1-4-1, 7-12-7, 5-1-5, 6-12, 6-1.
Arms-Two brass arms 6.5" (16.5cm) long with steel points are attached to lower part of semi-circle, one pivoted at centre the other fixed. Each fitted with two small sight vanes, each with a peep-hole sight and slit and graduated on face 2.12 and on back 4-7.
A recipiangle is used to measure angles; the sights are lined up with particular landmarks and the angle read off from the protractor.