In case you don't know how to determine the optimum nitro content for your motor—here is how it is done.
Fill the tank with the fuel to be tested. Start your motor and run it up at full throttle at your take-off mixture setting. After 15 seconds warm-up, touch the plug with your battery lead. If the motor slows down, reduce the nitro content. If it remains the same, or speeds up a couple of hundred RPM, you are at optimum. If it speeds up quite a bit, you need more nitro. After the test, check to see if your plug is still good. If the plug is burned out, re-do the test. Your goal is a fuel that speeds up only a trace with additional glow plug heat.
Extracted from a Fox Manufacturing infomercial, Model Airplane News, August 1987, p49.