I am remaking the ITPs so that they will work on all modern browsers and tablets. They will remain freely available to all without the need for a subscription.
This ITP simulates a 100-bead string. You can move all the beads to the right of the string and move individual or groups of beads to the left side of the string by clicking on selected beads. The controls also allow you to move 1 or 10 beads to the left or right of the string to show addition and subtraction. This ITP can be used to model different counting and calculation strategies.