In 1993 Neal Spruce tested Flex's bodyfat with a "Skyndex" brand electronic skinfold caliper, using the "Durnin" calculation formula on the number 2 setting (active male/athlete). Two weeks out from the show he tested at approx. 1% and the following week when tested the Skyndex displayed "E E E" which means "error". Which means that his bodyfat was less than 1% according to the device. The Skyndex is not capable of measuring less than 1%. It will display the error message.
I was an eyewitness to the test by Neal. Whether Flex had Billy Smith retest him at Gold's to confirm the reading I do not know. However, it is entirely possible.
The Durnin formula tests four sites: Biceps, Triceps, Subscapula and Illiac Crest (Abdominal area). It is definitely the most accurate of the skinfold measurements. However, it is not as accurate as Hydrostatic Weighing or the new Body Scan.
If any of you have a copy of the '93 Mr. O, take a look at the striations in Flex's back. It will be the freakest and leanest you have ever seen!
I have personally tested THOUSANDS of people's bodyfat (including some of the best pro bodybuilders in the sport) with the same device and I have NEVER seen someone lean enough to cause the device to ERROR the way Flex did. So wether he was truly less than 1% or not, I highly doubt anyone has ever tested leaner, Andreas Muntzer would probably be the only canidate.
FLEX IS AWESOME! Can't fight it!