Usage: Move and resize the red rectangle until it precisely covers the screen element you are investigating. Use the sliders for large movments. Resizing is always on the right and bottom edges. For pixel-precise positioning, use the cursor keys. For precise resizing, use PageUp, PageDown, Home and End (laptop users: try fn + cursor keys). You can then read off the values in the black square and in the title bar. The smallest screen element that can be measured by this app is 54 x 13. Seems like a weird number, I know, but that is as small as yab can shrink a window. The maximum size is a quarter of your screen. Finally, pressing the R key will reset the app to its original state (for example, if you've moved the red rectangle off the screen), and you can press Q to quit.