We have seen at the beginning of this course, how important distance and angles are for geometry. This was historically extremely important. Applications were in military, geodesy or even finance for calculating interests. The Harvard Putnam gallery of scientific experiments one of the three still existing compasses designed by Galileo Galileo. Invented in 1597, the instrument is linked also to mathematical instruction. Between 1598 to 1604, Galileo taught various noble men like the Duke of Mantua on the use of the instruments. Galileo was also an entrepreneur and made quite a bit of money by selling the instrument.