- Same scale, same time, same way.
- Weigh in the morning, after the toilet and before food or drink.
- Bare feet on a hard, flat floor.
- If your soles are dry, damp them or wipe the plate with a damp cloth.
- Stand still, weight even on both feet, until the reading settles.
- Answer the bowel question.
- Read the 7-day trend, not the morning.
Why the current needs damp feet
A bioimpedance scale sends a small, harmless current up one leg and down the other and measures the resistance it meets; water-rich tissue conducts well and fat conducts poorly, and from that and your height, weight, age and sex it estimates body fat (Kyle 2004). Dry, hard skin is a poor conductor. The scale either fails to read or treats the extra resistance as fat, so a dry-footed morning can read two or three points high for no reason. A damp sole, or a damp cloth over the plate, fixes it; some makers say so in their own instructions.
Why the same time
Every number the scale estimates depends on how much water is in you, and that changes through the day with every drink, meal, session and trip to the bathroom. The morning after the toilet is the most repeatable moment you have. A reading after a hard session, a sauna, an evening's alcohol or a salty dinner is a reading of water; VT asks you to log the first three so it can discount them.
Why the bowel question
The current crosses the trunk, and a full bowel changes what it meets; a morning without a bowel movement reads heavier and shows more visceral fat (Why VT asks about bowel movements). Marking it lets VT read the morning for what it is and lets the energy engine discount the weight.
Why the trend
Weight moves 1 to 2 percent from day to day and scale body fat 2 to 3 points, on water alone (Why your weight and body fat wobble). Neither is fat gained or lost overnight. VT draws the 7-day weight trend and the 14-day body-fat trend and reads those; its energy engine estimates your weight change by regression over the whole window, never by subtracting two mornings. If you have a DEXA scan, VT corrects the scale's body fat against it, so the daily trend sits on a calibrated level.
What not to compare
One scale with another (each has its own algorithm and its own bias of several points; Bosy-Westphal 2008), the visceral-fat index across scales, or your scale with a friend's. A new scale starts a new series in VT.
Women
The week before a period reads heavier and wetter on every line of the scale; VT reads the cycle you log and offsets it in the energy engine, and the trend absorbs the rest.
Sources
- Kyle UG, et al. Bioelectrical impedance analysis, part I: review of principles and methods. Clin Nutr 2004;23:1226–43. doi:10.1016/j.clnu.2004.06.004
- Bosy-Westphal A, et al. Accuracy of bioelectrical impedance consumer devices for measurement of body composition. Obes Facts 2008;1:319–24. doi:10.1159/000176061
- Vitality Tracker, How Vitality Tracker estimates your energy expenditure, method note v1.0.