Bit sized bits here. Feel free to consolidate or otherwise optimize.
Trap the initial field as character, named "Pre Length". Now we need some calculated fields:
Pre Inches (character):
That, er, measure up for you?
Edit: I missed factoring in the inches, and dividing inches+decimal by 12 to get decimal feet!
So close and yet so far!
Final Length field should be:
The Feet formula becomes:
The Final formula becomes:
It would be nice to convert it back, but since you wouldn't be able to use it in a measure for a summary anyway it doesn't matter. I can easily do that part in Excel.