The Most Reflective Mirror Is Made from Transparent Plastic

The GNU Units program knows 3523 units, ranging from commonplace to extremely obscure, supports 112 nonlinear units, and common mathematical functions. In 2019, I built a Web interface wrapper, Fourmilab Units Calculator, which adds the ability to define and reference variables used in calculations and automatically updates currency exchange rates and precious metal and Bitcoin prices daily. The link above shows examples of scientific and engineering calculations done with Units Calculator.

I’ve been interested in calculation with physical units for a long time. In 1967, I partially developed an extension to the ALGOL programming language that kept track of units in computations and detected dimensional incompatibility in expressions, and in 1993, patented a similar scheme (U.S. Patent 5,253,193: Computer Method and Apparatus for Storing a Datum Representing a Physical Unit), the story of which, including the original disclosure of the invention and what came out of the sausage machine four years later, is told in “Talkin’ 'Bout My Innovation”.