Mathcad express/free trial provides incorrect solution

[jwpeters]

I try adding 355.302°F+9°F which should equal 364°F. However, mathcad keeps giving me 823.972°F. It doesn't care if I use the variables or direct numbers.

[LucMeekes · Accepted solution]

You're using the wrong unit for temperature difference.

Note that:

If you add two of those, you end up with temperatures above 500 K.

Use DeltaF for adding/subtracting temperatures.

Success!
Luc