Click to set a base point and move your mouse around to make a box. It has a "X" in the center as to visualize the length of the line. The variable in the top left corner is the length of one of the light blue lines. See the variable in decimal by holding down any button.
This was a quick project that I whipped up to put some math stuff into use. I think it looks pretty cool. I used Pythagorean Theorem to find the length of the hypotenuse (or one of the light blue lines). (A²+B²=C²) The reason that script looks so long is because I didn't want to use multiple variables to find the length. I also rounded it so it didn't take up half the screen, but you can see it in full decimal by pushing down any key. Update: Made math into one "set variable" block