Zebestov It will be very useful feature, especially in position fields. So we can write: "123.45 - 150" and get the correct number instead of calculating it in the mind or with calculator.
Nate Currently we allow math using the current value by entering +123 and +-123 (note subtraction is done by adding a negative number, since starting with minus is for negative numbers), /123, and *123. I agree arbitrary math would be nice. Here's the task for that: https://waffle.io/EsotericSoftware/spine/cards/580bacfc29fef328007f9dc8