Thank you Vexiphne!

I think it works how it should for the purpose. It's for a tiled image that usually isn't at scale 1/1 to begin with. The problem with tiles is that you can't really see what they look like in the preview window - you need to do a quickie render to see them correctly.  So a user could render and then say - I want it whatever percent bigger or smaller. And adjust according to the render. It all hinges on the size of the object vs. the size it is in the render (think of a dress vs a little arm band) and that along with how much room it takes up on the UV plane.

I waffled back forth about the percent vs the decimal factor (90% or 0.9), and figured percent might be more what people are used to.

Anyway, big ramble.. :)   thanks for testing it for me.