I am a huge Sethbling fan, and after I watched his Mega blocks comparator I thought
it would be fun to build my own Mega block comparator, only a bit improved:
it can do all thinks a comparator does, and on the same way, but it is slow;
it can take 15 seconds to subtract signals.
to switch between compare and subtraction mode, use the button on the front torch.
the comparator is in subtraction mode when the lamp is lit.

this comparator is made in a 48:1 scale, only with this size I could get the redstone
inside without cheating.