Lghtmtr is an incredibly simple light meter app to measure the amount of available light to determine the proper exposure for a photo.
Because of its simplicity, Lghtmtr is a great learning tool for students and those new to film photography to understand how exposure, aperture, ISO are interconnected as the app helps the user better visualize these connections.
Take a reading of a scene, and then the initial exposure settings are shown. When you adjust one value, the other values will update. At any time you can lock a value from changing. You can also review the image which your exposure settings are based on.