Relativator
From Wikipedia, the free encyclopedia
The relativator was a pre-calculator era circular slide rule designed to perform calculations of Einstein’s special theory of relativity.
It was produced by Atomic Laboratories, Inc. It was mailed to buyers in an envelope with words printed on it that said “Enclosed is your Relativator!”.
As calculators and computers eclipsed older technologies such as slide rules, the relativator slipped into oblivion.