pass value back to o subroutine based on radiobutton setting?

Thanks to andypugh's excellent example setup here: www.bodgesoc.org/lathe/lathe.html , I was able to get some pyvcp spinbox values back into my code.

Now I'm trying to implement a similar setup with a radiobutton but getting a bit/float mismatch error:
custom_postgui.hal:11: Signal 'ztype.Plate_in' of type 'bit' cannot add pin 'motion.analog-in-01' of type 'float'

So the cause of the error is obvious to me, but the solution isn't as clear (at least not for a pyvcp/python noob like myself)

Here's my current XML code:
In the postgui i have:Which works fine for a spinbox value, but not a radiobutton.

Basically what I want to do is have different offset values passed back into the o code depending on which radiobutton is checked.

so simple.
thanks Andy!