Convert degree rankine to degree celsius

Common temperature conversion mistakes

• The Celsius-to-Fahrenheit formula is °F = °C × 9/5 + 32, and the classic mistake is forgetting the +32. The multiplication alone turns 20°C into 36, but the correct answer is 68°F. Going the other way, reverse the order: subtract 32 first, then multiply by 5/9.
• The +32 offset applies to temperature levels, not to temperature differences. A change of 10°C equals a change of 18°F, just the 9/5 factor, no offset. Adding 32 to a difference makes every change 32 degrees too big.
• A common mistake is rounding the Celsius-to-kelvin offset to 273. It is exactly 273.15 degrees, so 25 °C is 298.15 K and absolute zero at −273.15 °C is 0 K. Kelvin also takes no degree sign, so write 'K', not '°K'.
• Fahrenheit usually shows a bigger number than Celsius, but not always: the scales cross at −40°, where −40°C equals −40°F exactly. Below that point Fahrenheit reads lower than Celsius. The crossing point makes a handy sanity check for extreme cold.