What you see in front of you, is the Magdeburg slide rule, developed by Johann Philipp Gruson, a great uncle of Hermann Gruson. His calculator made it easy to calculate, because it only needed to be read. There are 9 circular sectors on the disk for the numbers 1 through 9. You can do all 4 basic operations. The first two columns are for addition and subtraction. The remaining columns are used for multiplication and division. Try out the tasks on the accompanying poster. Can you solve them all?