The user of the DC chooses an option ( in this case 32'' or 42'') these are two options , so I would assign the values of those options in the Attribute's list options dialog.(1 and 2)
You could then easily choose the corresponding Height (in LenZ) and Width (in LenX) with the CHOOSE-function.
CHOOSE("option number of User selected choice", "Heigth if option number=1","Height if option number=2")test tv3.skp (233.1 KB)
Combining the two functions would give:
CHOOSE(OPTIONINDEX("User's choice in INTEGER number"), "Length if User chose option 1", "Length if user chose 2")