This is a nice little utility. Could I suggest an enhancement?
Use "gr+" to calculate the values in increasing values.
Use "gr-" to calculate the values in decreasing values.
As a designer, I need to use both from time to time. The "+" value is simply multiplied by 1.618, while decreasing is .618. I'm not a coder, so I'm not sure how to make it work, but it seems fairly straight forward.
Anyway... thanks for creating and sharing your work!