Summary

I've taken an interest in analog computing devices, both electric and mechanical. Here is a simple one, modeled after a similar device from long ago.

To use it: suppose you have a recipe that makes X servings, but you want to make Y servings, and you want to know how much of each ingredient to use. On the "recipe servings" scale, find X; on the "desired servings" scale, find Y; move the slide until those two align. Then for each ingredient, find the amount on the "recipe amount" scale, and read the corresponding amount on the "actual amount" scale.

For example: suppose a recipe makes 4 servings, but you want to make 8. On the "recipe servings" scale, find 4; on the "desired servings" scale, find 8; move the slide to align those two, as in the photo here. Then if the recipe says 1-1/2 cups flour, on the "recipe amount" scale find 1-1/2; read the aligned value on the "actual amount" scale: 3 cups. If the recipe says 3/4 teaspoon vanilla, on the "recipe amount" scale, find 3/4; read the aligned value on the "actual amount" scale: 1-1/2.