You can do math in your head, instantly. If your character has this talent, then you, the player, may use a calculator to figure anything you want at any time, even if your character is fleeing for his life! Alternatively, for simple math problems and well known higher problems, the GM may just say the character knows the answer. You also get +1D on all astrogation checks or any other checks requiring or able to use fast mental math, not necessarily all repair skills.