On the Use of this Book.

of the staff, which one may see quite clearly. From this, one line goes through the middle of the sighting hole, like OP, and the other just as much higher as the ear on the top small cross-piece is wide, like QR. So between those two parallel lines, everything is white

makes it; it will be better and more useful for the intended purpose. This graedboogh quadrant/degree-arc being thus perfected, the use thereof to take the altitude with it is as follows: One sets it with the back toward the Sun, (as in the figure here alongside) and looking through the

A woodcut illustration demonstrates the use of a cross-staff (Jacob's staff) for solar observation. A man in a cap is shown in profile, holding the staff to his eye while facing away from the sun. The staff has a horizontal main beam with numerical markings (90 to 20) and a vertical transom. Dotted lines indicate the lines of sight: one from the eye through the lower sight to the horizon, and another from the eye through the upper sight towards the sun, which is depicted as a face with rays in the upper right. Three decorative floral fleurons are scattered in the sky area.