Counting House

sums in your head · twelve a round · harder as you get better
Counting House

Add, take away and multiply in your head. Twelve sums a round: get eleven right and the next round is harder, seven or fewer and it is easier.

Keys: 1 to 4 answer · Enter starts a round

An engraved table of the digits 0 to 9, each drawn as an object
Arithmetic characters · Robert Fludd, 1617