This small tool is very handy when studying a (road) map. Rolling over the small wheel, handling this instrument like a pen, will make the hand move in the round part. When you start the hand on top and select the correct scale / ratio you can read the exact amount of kilometers in real life. Nice chromium plated shiny tool with plastic windows (scratch free) in the original box. No makers mark but European made around 1950, probably in Germany where I found it. The snug fitting box measures 12,5 cm or 5 inches long. Check the video for a vintage desk stuff collection!