I have just purchased a Sekonic Auto Reader II light meter. It’s comprised of two main dials that have aperture and shutter speed on them, and also it can indicate ASA (ISO) and DIN. These dials are lined up by using the needle indicator underneath them. The green needle has a diamond shaped hole in it for the red needle to be lined up for correct exposure readings. Once the needles are aligned the dials have a silver and red indication painted on them, so only numbers that line up in the silver section can be used for a good exposure. The aperture and shutter speed numbers are matched in pairs so this gives a range of working aperture and shutter speed combinations.