"Counting in their heads" - 1895 oil painting

[EdS2]

It is a calculator forum, but there's an intersection: the prodigal calculator. This is W. W. Rouse Ball writing about George Parker Bidder:

Quote:Halfpence rewarded his efforts, and by the time he was eight years old, he could multiply together two numbers each of six digits. In one case he even multiplied together two numbers each of twelve digits, but, he says, "it required much time," and "was a great and distressing effort."