This technique was developed from mere laziness. I've been shooting a new digital camera with more bells and whistles than I've been able to absorb. So I set the thing on full auto program, mounted an IR filter on the pop-up strobe, and began shooting to a Firefly-slaved strobe. When the first exposure came up on the viewing screen it was clearly over exposed. We moved the slaved unit further from the subject and tried again. Still too much light! Well, heck, the strobe sherpa simply covered up 1/3rd of the output lens with his fingers and we shot again. Voila! Photography made simple. We quickly devised a simple shoot-and-review system, and I called for the needed percentage of light required per the proof. Guide-number-math be damned! It worked very well. We dubbed the technique "Flintstone" for the obvious bone-headed, archaic reason.