Microscope calibration tool.

Fullsize image: https://diqn32j8nouaz.cloudfront.net...l_fullsize.jpg



Previously:

1860s British brass microscope - photo
Rife No.3 universal microscope - photo
Drilling lead under a scanning electron microscope - GIF
Wood under an electron microscope - photos
Drilling lead under a scanning electron microscope - GIF
Cast iron microstructure magnified - GIF