I have created my own version of this ITP which allows you to find the difference between two numbers and shows this on a number line.
View full screen in your browser. 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.
This resource is freely available to download from the archived Primary Framework site.