I too would like this. It takes too much time to switch to a separate calculator to figure out a complex circle's radius. I thought the /2 idea would work but it doesn't I have a Sketchup model that is set to decimal inches. I keep trying to draw a circle with a 1.25" diameter. If I type 1.25/2 in the box I get a circle with a radius of 1.25. I've tried a number of different ways of typing this to no avail.

Bummer.

I don't remember this happening before today but it's happening now. On Mac 10.8 running Sketchup 8. When I switch to the calculator app all the smaller windows (tools, components, entity info) disappear. I'm trying to do some math based on the entity info but when it hides like it does I'm kind of out of luck. Any thoughts?