Don’t feel like shelling out $5 for a fancy factory made calculator ... addition and subtraction, this is a great way to make sure you really understand digital logic. Take a look at the rough ...

and follows a decimal design in which the rotation of a gear with ten teeth represents the numbers 0 to 9. We’re taken through the mechanical processes behind addition, subtraction ...

which let field engineers swap out defective circuits for working ones. Presumably the same modularity let the design team replace all the vacuum tubes with transistors. The resulting calculator ...