This looks like a first-rate tool that will do anything a modeler ever needs involving scale calculations - and then some. I'm in awe of the sort of brain that can design such a program.
The only problem I can see is that, if I understand the program correctly, using it requires a computer. I've toyed around with the idea of buying a notebook computer and taking it out to the workshop, but there are some arguments against that approach. (The big one is money.)
There's a cheaper, practical approach: the pocket calculator. I'm sure it won't do everything Mr. Crenshaw's program will do, but it probably will be more than adequate for the sort of math that has to take place in the modeling room.
About fifteen years ago, if I remember right, some electronics company introduced a pocket calculator called "Modelcalc" that was designed specifically for model builders. It wasn't on the market long; I guess it didn't sell. Several companies, however, are now selling calculators that operate in feet, inches, fractions of inches, and metric units. I have the impression that these gadgets haven't caught on in the hobby world, but they're quite common among woodworkers, carpenters, and the construction trades.
The next time you're in your local Lowe's or Home Depot, take a look at its measuring tool section. You'll probably find four or five different calculators, with prices ranging from about $15 to $50. The cheapest one probably will do everything a modeler needs. (The more expensive ones have dedicated keys for things like calculating board feet of lumber and rafter angles.) All you're likely to need in model building is the ability to enter units of measurement and perform basic arithmetic. If, for example, you know something is 43' 7 3/4" long and you're working on the scale of 1/4"=1', just key 43' 7 3/4" into the calculator and divide by 48. (The answer, according to my calculator, is 10 29/32".) Most of these gadgets also have conversion keys that convert between the English and metric systems with one keystroke.
Another useful electronic gadget, though a little more expensive and harder to find, is the digital caliper. Woodworking supply companies, such as Woodcraft ( www.woodcraft.com ) or Lee Valley ( www.leevalley.com ), now sell these wonderful instruments at pretty reasonable prices. (I think I paid about $40 for my 4" one. As far as I'm concerned it's paid for itself.) If you do go to either of those sites, be prepared to stay awhile. Woodworking and modeling have a great deal in common. I've bought dozens of tools from those folks.