Lovely, very useful – Hands-On Math Hundreds Chart Review

Seems to have an arbitrary limit on the number of markers that can be placed -- so it's difficult to demonstrate the Sieve of Eratosthenes using a different color for each multiple of the first few primes. Also, removing a marker is difficult and haphazard. An undo button would be useful in addition to the eraser button which clears ALL of your work. Overall, a very handy app for teachers. I'm grateful.
Review by Tracy Dower on Hands-On Math Hundreds Chart.