Well, I've "just followed directions with attention to detail" (honestly taking all the hits the way I read the instructions), and plugged the measurements into the SCHRS spreadsheet. The end result is that I get an SCHRS rating for a 1-up Isotope of 1.050. That is essentially the same as (marginally faster than) a Viper 1-up with spinnaker.

How in the world a 52 year old design without a spinnaker is supposed to beat a 6 year old design with a spinnaker is totally beyond my comprehension. There's no way I can sail the boat to that rating, so I guess I'll stick to one-design and Portsmouth Yardstick racing.