I needed a tool to measure distances on-screen and wrote this quick program. Other apps that fulfilled my need were either costly or listed on sketchy-looking websites. Use the white boxes in the lower right-hand corner to move and resize the ruler. Scroll on the ruler to measure magnified images. Match the magnification label (i.e. 'x5') with the magnification of your image (i.e. 500%). This is helpful when measuring small distances accurately.