There’s a good chance you once had to learn how to convert from Fahrenheit to Celsius and vice versa. There’s an even better chance you have forgotten to do so. Do not be ashamed! Once upon a time Gothamist taught eager young minds how to do the conversion. Alas, time has taken its toll and Gothamist no longer remembers the equation.

Santorio Santorio is credited with inventing the thermometer. Daniel Gabriel Fahrenheit was the first person to use the more accurate mercury thermometer. Fahrenheit assigned the freezing of a water/salt mixture as his zero degree point. He then set human body temperature to be 90 degrees. With improvements in thermometers and a change in scale, the Fahrenheit scale with which we are all familar (water freezing at 32 F and boiling at 212 F), came into being. Anders Celsius devised a temperature scale wherein water froze at 100 C and boiled at 0 C. That is not a typo. A year later the scale was reversed. By the end of the 18th century thermometers were much easier to make and there were several hundred temperature different scales being used in Europe!

Luckily, there is an easy way to convert temperatures when the weather calculator is not handy. An eighteen degree Fahrenheit temperature change equals a ten degree change in Celsius. Starting from 32 F equalling 0 C, 50 F must be 10 C, 68 F equals 20 C, 86 F is 30 C, and so on. Still too complicated? Not accurate enough? Get a dangerous pocket thermometer to carry with you.

As you can see, it was 78 F, or 26 C, in Gothamist’s apartment when this was written. It was also 22 on the Réaumur scale, but let’s forget about Réaumur. Afterall, everyone else has.