Reticles are clear glass discs marked with scales or patterns, which fit into microscope eyepieces at the internal real image plane. This is the intermediate image of the specimen/object under inspection produced by the objective lens of the microscope. By placing the reticle at this position, the scale/pattern is superimposed on the image and both are in simultaneous focus. These reticles are all designed for an objective power of 1X. Squares are numbered 1-10 horizontally and lettered A-J vertically.Note: 19mm version is not numbered or lettered.