Source and sensor integrity

Check whether the source is primary, competent, properly calibrated, and free of incentive contamination before trusting its output.

Your new smart scale announces that your body fat dropped 3% in ten days, and you're ready to credit the new routine. Before celebrating, look at the messenger. Consumer scales estimate fat by running a current through your feet and guessing from water content, so a salty dinner or a dehydrated morning moves the number.

The move is to audit the source before trusting its output: is it primary or secondhand, does the instrument actually measure the target or a proxy for it, is it calibrated, is the sampling consistent, and does anyone have an incentive to flatter you. Steps: identify what the sensor really measures (electrical resistance, not fat), standardize conditions (same time of day, same hydration state), check calibration against a known reference where possible, and note deviations and missing readings instead of ignoring them. When it works, you stop steering your health by a flattering instrument and either fix the measurement conditions or switch to a measure that deserves your trust, like a tape measure and photos. Don't audit endlessly when the source is already good enough for the stakes; a rough scale is fine for a rough decision.