This circuit is another must-have for all calculators. Binary subtractor (as you can guess from its name) can subtract two binary numbers. You can have some problems when you will try to build and use a subtractor - If you want to build up one for yourself, you can look at this scheme - A stands for minuend input, B stands for subtrahend input, BORin and BORout stand for connecting with previous/next full subtractor, D stands for output Or you can download this world file and test it yourself - Binary Calculator world file