The bead at the top of each column counts for 5 beads in the main compartment in that column. The beads in the main compartment of the left column each count for 10 single beads. The bead in the top compartment of the left column counts as 50.  But the top compartment is upside down in this app.  To learn the correct Abacus model, go to  Abacus Explained Properly in this collection:  http://euclidsmuse.com/app?id=1017.