Listboxes in Mathcad are created using a programming language (like VB or Java) and programming languages generally do NOT deal with, or handle, units. That is something different than saying that with a programming language you can create an application that DOES handle units. Mathcad is an example of such a computer application. It's written in C, while C does not handle units (well, not the units of measurement that we're talking about).
It's the same with Excel. This spreadsheet application is not equipped to handle units, but you can build a spreadsheet that contains units.
Anyway, I guess your only option is to make sure that you populate the list box with only values that are in inches, and introduce it on the screen as a list box with lengths in inches. Essentially this means: you cannot have mixed units in your list box. Upon return of a selected value, you multiply that value within Mathcad with the unit inch, and you're done.
Success!
Luc
