Zeiss Centrally-Symmetric Double-Image Ocular for Toolmaker's Measuring Microscope Circle
This is a Zeiss centrally-symmetric double-image ocular for use on Zeiss toolmaker's measuring microscopes. Reticule consists of a single circle. The centrally-symmetric double-image method allows rapid location of round holes and other centrally-symmetric features by splitting the microscope image into two images that, when superimposed, appear colored, unless the feature is precisely centered. Displacements as small as 1 µm can be detected with this method.