.NET

[#1]

Ok, I think I figured it out.  the integer required should be the denominator of the fraction of the precision required.  For example, 1/4" precision would require the integer 4 and 1/256" precision would require the integer 256.

If you want to use the drawing units,   just use:

Autodesk.AutoCAD.Runtime.Converter.DistanceToStrin​g(Dist as double) as string

[#2]

I had a similar situation once.  I found that the best solution was using Regular Expressions.  That way you can parse whatever the user puts in your text box.  In my case I restricted the units to inches, but they where free to write some like 10'-1 5/16", 5/32", 10" or 8.75".  

[#3]

Recently I used Converter.DistanceToString method and I would like to clarify two points for others.

1) Precision is integer from 0 to 8 (LUPREC equivalent). E.g. 1/4" is 2.

2) This method return value affected by AutoCAD variable DIMZIN. This variable controls suppression of zero. You have to temporary change it to your needs and then revers it back.