Refreshing Activex Textbox

I've built a spreadsheet with quasi-animation for a physics class on projectile motion. In it there's a animated chart showing velocity change as a function of distance. The chart has on it an ActiveX textbox that refers to a cell that contains a formula showing "V_y = {velocity}". I've tried a number of things to get the display of the textbox to change during the animation. If I break the code at the line that updates the cell referenced by the textbox the display changes. But I can't figure out how to get the display to update while the code is running.