Caloric Difference

if(prop("Burned") == toNumber("") and prop("Consumed") == toNumber(""), toNumber(""), prop("Burned") - prop("Consumed"))

if(prop("Burned") == toNumber("") and prop("Consumed") == toNumber("")

Check to see if both Burned and Consumed are blank (including no 0). toNumber("") is equal to nothing, as opposed to 0

toNumber("")

If they're both blank, return nothing.

prop("Burned") - prop("Consumed"))

If either have a value (including 0), subtract the Consumed value from the Burned value.