12. Animate using F9 key       & DO loop in EXCEL! NEXT Follow the instructions below: In the main menu, choose Tools ----> Option -----> Click the tab Calculation ----->Make the Maximum Iteration: to 1, and make sure the Iteration box is clicked on. Go to the cell C10 and type in the formula =C10+delta_t. and press enter key. This circular reference here is allowed as we have enabled Iteration in the previous step. Observe what happens when you press the F9 key! The F9 key (Calc Now) in EXCEL forces all the cells with formulas to be recalculated immediately, and this also results in new input to the chart and the graph is also moved according to the new value of t!. So if you keep that key (F9) pressed the whole sheet will be recalculated again and again and we will have the effect of the wave moving to the right as a function of time t. What we have done here is equivalent to a DO loop in a programming language! You can always reset the value of t in C10 to 0.01 (unfortunately not to 0) by rewriting the formula in the same cell and pressing the enter key. wave12