I believe you measure muscles flexed,not pumped but flexed.I always heard you measure the biggest part of muscle,but make sure the tape is perpindicular to your body part,not all angled.Arnold never claimed to have 24" arms.The only bb to have legit arms(that i've heard of) over 22" was ronnie coleman at 23 1/4".Everyone else claims 22" arms but I've heard most lie about height,weight,and measurements.Some guy who had strict ways of measuring bb's said Arnolds were 20something or 21something,and the biggest were sergio olivia at 22 even