Subscript variables when calculating values in Freeform

Subscript variables unfortunately don’t work when calculating values in freeform. For example, this:

See how I’m trying to use subscript variables? It simply doesn’t work. The correct answer is 840/1643, or 0.511…, and the answer isn’t supposed to be in degrees celcius. Can this functionality be added into freeform? Subscript variables are heavily used in physics and other math subjects, so this would be a great plus.