One of the full page illustrations
in Cosmographia is this circular calendar. The outer
scale shows the Zodiac, each sign divided into 30 degrees. The
lower left quadrant of the inner disc can be used to tell the
time in unequal hours, which were widely used in the 16th century.
Because unequal hours divided both day and night into twelve
hours each, these hours varied in length with the seasons, as
do day and night. The right quadrant shows a shadow
square, a proportional
measuring device often used to measure
heights at a distance.