If you'll allow me to rant for a second here, we shouldn't even need this mnemonic, because Celsius is objectively a much better temperature system. 0 and 100 are conveniently based on water's freezing and boiling points. Beautiful! Fahrenheit makes no sense at all. Daniel Gabriel Fahrenheit based his thermometer on a temperature scale where 0 was the temperature of an ice, water and salt mixture and 96 was body temperature, according to LiveScience. He was wrong about body temperature, so the scale was shifted a little bit so that 32 Fahrenheit lined up with water's freezing point and 212 Fahrenheit lined up with water's boiling point.

Fahrenheit is now essentially just a percentage of how hot my grandma feels where 100 is 100 percent hot or "it's so hot I couldn't even sit on the boardwalk," 50 is 50 percent hot or "not too hot, not too cold. It's chilly," and 0 is 0 percent hot, or "oh, it was so co-old I had to take the car service to the supermarket."

The 6 train mnemonic has been around since at least 2006 according to Gizmodo, originally posted by railroad.net user Fred Rabin. It works because the 6 train stops every 9 or so blocks. Celsius has 100 tick marks between freezing and boiling, while Fahrenheit has 180, and the ratio of 100 to 180 is 5/9, sp five degrees Celsius equals 9 degrees Fahrenheit. That's where the "5/9" comes from in the silly "Celsius temperature is the Fahrenheit temperature minus 32 times 5/9" trick.