An apparatus comprises an inflatable vehicle occupant protection device and a gas generating material that, when ignited, produces gas to inflate the inflatable vehicle occupant protection device. which is capable of miniaturizing the size, and preventing moisture, etc. The boundary area for displaying the icons on the computer screen is calculated. Adaptation of the method to widely differing wavelength parts of the electromagnetic energy spectrum is included. Thus, it is possible to automatically and accurately measure the film thickness of the flux in the transfer area without requiring any complicated measurement work.