The instrument comprises a circle hollowed with one solid quadrant. The limb of the circle is engraved with a scale of hours, divided to 1/2 and 1/4 hour, numbered from 1 to 12 twice and from 1 to 24. The inner part of the circle has a quadrant with the other two radiuses connecting the centre to the circle, sliding in a groove inside the circle itself. The quadrant is engraved on a straight edge with a scale divided to 1/2, numbered from 1 to 9 and on the limb with an equal scale from 1 to 12 divided to 1/4, numbered from 1 to 12. On the quadrant are lines extending from the straight edge. A radial arm is fixed to the centre of the protractor, and is engraved with the same scale as in the square edge of the inner quadrant, numbered from 1 to 12. The back of the instrument is blank.
