text: I'm not sure I understand your question, but if you are talking about when you receive an xray, there is no special formula. The technique used has many variables. Some of the many things to consider when taking an xray... body part, thickness, distance, kilovoltage, milliamperage, seconds, type of tube, type of film, type of screen, and many, many others. Every technique is different. But when someone sets the control panel, they are selecting the kilovoltage peak and the milliamperage seconds.