It's been a while since I've seen a device quite as engaging as this entirely mechanical calculator, the "Curta," designed by a prisoner in the Nazi concentration camp at Buchenwald. Elegant and designed with extraordinary (quintessentially German?) precision, the unsettling fact is that it could have given German field artillery a huge advantage had its design been completed before the camp was liberated by the Allies. Yet with the characteristic neutrality of many devices, whatever their potential misuse, it is essentially beautiful in its own right, a triumph of ingenuity under many kinds of pressure.