The Apex Scaler allows you to measure things with a microscope. To do this you will need an eyepiece with a scale in it which called a measuring eyepiece, and a slide with a microscopic ruler etched on it which is called a stage micrometer. The Scaler kit contains both, together with instructions on how to do it. The measuring eyepiece for the Explorer Plus stereomicroscope is of course different from the measuring eyepiece for the high power microscopes, but we will sort this out for you when you order. Just make sure you tell,us which microscope you have