An Array of Abacuses

 My dad collected manually-operated adding machines. His drafting work often called upon him to add up numbers, so he had at hand a hand-cranked adding machine with dozens of buttons, also one of those plastic turn wheel adding machines that you had to use a stylus to turn the wheels, and he also had three (or more)  abacuses (the plural of abacus), those featuring sliding beads that a skilled manipulator could use to add up totals very quickly. 

In fact, that is what my dad used when adding up orders and sales tax for his hot tamale sales business. Here is a picture of three of his abacuses. 

Click on the image to make it larger.

He also had a selection of slide rules of various sizes, even a circular one. Those came in handy for multiplication and other more complex mathematical calculations. His day job was a piping run draftsman for a chemical plant in Ama, La., so he did a lot of measuring and computations comparing plans for piping runs to actual as-built piping runs between processing units in the plant. 

All these were prior to the coming of electronic calculators, both the desk models and handheld kinds. I remember the first handheld calculators, they cost several hundred dollars. The "scientific calculators" cost even more. Now they give them away as souvenirs at trade conventions. 

Slide rules