Read the entire help entry carefully before using the Change event. It fires for every character typed into the field for one thing so anything you do will be executed for each character that the user enters. Plus it doesn't always fire when modified by other methods. You need to explicitly referenct a control's .text property. From help:
Setting the value of a control by using a macro or Visual Basic doesn't trigger this event for the control. You must type the data directly into the control, or set the control's Text property.