Dimension Diameter for revolve

Hi all,

I would like to be able to dimension using the diameter as a parameter, not the radius, is there any way to dimension it like in the attached picture? At the moment I have to divide it by two when entering the radius, which does not retain that relation unless I manually create a formula every time. I know I could draw an extra line with a mid-point relation but it seems like more work than should be required for something so simple..

There must be a better solution, any ideas?

Cheers,

Stew