This is a unusual style vernier speed gage/caliper that is spring loaded for quick production inspections. It is marked "CHICAGO DIAL INDICATOR CO. CHICAGO ILL." Like most vernier gages, the user will take a reading at the cross points of the .025" line and the 0 - 20 scale as in photos. So, depending on your eyesight you should be able to take quick readings within about +-.005". It is adjustable, so you can adjust the probes to your liking. Range is .05" to .50. I have not seen one of these calipers by this company before, so we are selling it as a rare instrument from the mid-1900's era. It's made of steel, has some minor staining and pitting in some small areas, overall very nice shape.