The accuracy vs consistency trade
DEXA is accurate (±1–2%) and expensive; smart scales are cheap and noisy (±5–8%, hydration-sensitive); the Navy tape sits between (±3–4%) with a decisive advantage — measurement consistency you control. For tracking change, which is the actual use case, a consistent ±3% instrument beats an accurate one you visit annually.
The five-minute protocol
Morning, post-bathroom, before food. Tape horizontal, snug without compressing, mirror-checked. Neck below the larynx, waist at the navel, hips widest (women). Three repeats each, average them, write down the conditions. Same protocol every month — the protocol IS the instrument.
What to do with the numbers
Track the trend, not the truth: the absolute percentage may drift a couple of points from DEXA reality, but a month-over-month drop of 1% is a real change regardless. Pair with the lean-mass calculator to convert progress into the two lines that matter — fat falling, lean holding.