Most computer games with mouse aiming have a sensitivity value that decides how sensitive your aim is to your hand movement. If you want your aim to be consistent, you want the same sensitivity across all games so you don't have to relearn your aim for each new game.
Unfortunately, mouse sensitivity is a tricky business. Most games have their own sensitivity number, so you cannot just copy the sensitivity value from one game to another. Besides, your mouse DPI (which you can change in your mouse software) also influences your actual in-game sensitivity, making it hard to compare your sensitivity with others.
This calculator helps you convert mouse sensitivity between games. Just pick your games and enter your sensitivity.
If you type in your mouse DPI, it also shows how many centimeters (or inches) of mouse movement it takes to make a 360° turn in game. This is a better way to compare your sensitivity settings with others.