Vintage German Engineering & Mapping Inch to Foot Conversion Tool

"The Alvin Two-Face Inch Counter is a useful distance measuring tool for technical plans, drawings, blueprints, and many more. Its one side is equipped with a special dial for exact measuring of straight lines and curves. Functioning as a conversion tool, its pointer indicates traced distance in inches while the counter disk registers it in feet The second dial of this two-face inch counter measures distances on maps and plans with scales of 0.5", 0.25", and 0.13" to a foot. It also counts the number of full pointer revolutions"