Learn the shortcut! You can mentally convert between Fahrenheit and Celsius in 3 or 4 quick steps. It's easier to use than the exact equations involving 5/9 and 9/5 fractions, while still maintaining a maximum error of about 1 degree (+1%) in the worst case! Please note if you are testing in the Actions on Google simulator that there is a known bug with negative numbers if you type with the symbol "-". Instead, literally type "negative".