Celsius or Fahrenheit

Before I left for my mission, my wise older brother who had also served a mission in Europe gave me a piece of great advice. When it came to temperature, just keep in mind that roughly 20 degrees Celsius is 70 degrees Fahrenheit. That was all it took for me to know whether or not to bring a coat with me as I knocked on doors.

(25 degrees Celsius is 77 degrees Fahrenheit.)