In all honesty, there are several ways to measure a sail. There are very simple methods and exceptionally complex methods. A computer, that is giving you the exact computed sail cloth area, will deviate significantly from any simplified point to point manual measurement system. You can only get a precise manual sail measurement if you use a lot of calculus and intend to spend a few days on it. Manual sail measurement systems make an approximation of the sail area and good sail makers not only understand exactly what measurement system is specified by a particular class but how to wiggle in a little extra sail area and still measure in.

You need to know the sail area and the method used to measure it before you can really compare sails. For instance; the F18 class used to have their own sail measurement method before they became an ISAF class and had to adopt the ISAF measurement system (which was a little more complex and time consuming). Just laying sails on top of each other will not give you a very good picture of how they "measure in".

But, again, we're seriously splitting and resplitting hairs here.

How does SCHRS handle non-factory sails?