Change Cell Values The Change Cell Values window provides a means of editing an overlay. Suppose you would like to double the transmissivity for a group of cells. Select the cells and enter the number 2 in the Factor text box, then click on the Change button. All values in the selected cells will increase by a factor of 2. The Change Cell Values window works in any property overlay that has values assigned to each cell. This window greatly assists in performing a sensitivity analysis of a model.