>>Another client makes rectangular covers for swimming pools.
>>In that industry there is no measurement that is less than one inch- also by convention- so I carry all dimensions as feet and inches and print them as, for example, 11'6"X10'8".
>>I could have carried them as inches, and that would have made some calculations simpler, but I opted for feet and inches to simply things like data binding, reports, etc.
>
>SI based units are worth it. :)

That's one thing I learned over there... just keep everything internally in SI, convert when touching the surface. IOW, let them enter their inches, ounces, stones, feet, knees and what not, save as these separate units to display again if they want to check it, but have a separate field where it's kept in millimeters, kilograms, grams or whatever measure is appropriate. Do ALL the calculation in SI, display the end result in them stones, grains and 12+12 hour days. DO NOT try to calculate anything in these units.

http://ndragan.com/szajt/KUBNE_STOPE.JPG