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Mental Calculation. In Public School of S. A. Rachinsky - Nikolay Bogdanov-Belsky (1895)
(upload.wikimedia.org)
Wander the gallery. Look at the art. Be polite. If you feel able please post some great art :)
I wish I'd spent more time as a kid doing mental math.
I'm terrible at it, but it is a useful skill despite having a phone in my pocket almost all the time.