Carrying the Standard: A Sized Design for a Portable Field Calibration Kit for Market Inspectors

An inspector who visits a market on foot or by motorcycle can only certify what they can carry. This paper sizes a complete field calibration kit from its targets outward. The stated targets are to certify a market scale to 0.5 percent of load at test loads from 0.2 kg to 20 kg, and a volume measure to 1.0 percent at 1 litre and 5 litres, under a stated sizing rule that each standard's own error must be at most one third of the tolerance it is used to certify. The mass arm is a nine-piece set of class M1 weights from 20 kg down to 50 g whose published tolerances sit about 33 times inside the requirement at every load; the set's nominal mass is 38.85 kg and its largest composable load is 38.85 kg. The volume arm is a 5 litre and a 1 litre prover, with computed root-sum-square budgets of 9.0 mL against a 50 mL tolerance at 5 litres and 3.2 mL against a 10 mL tolerance at 1 litre. The whole kit — weights in two cases, provers and bench instruments in a bag, on a trolley — has a computed total mass of 55.05 kg, with a heaviest case of 33.00 kg that must travel on the trolley and never be lifted as a unit. A full stall inspection is costed at 36 minutes under stated time assumptions, giving nine full stalls in a six-hour field day, or 23 scale-only checks. The kit's verification chain — annual laboratory calibration, an assumed drift of 20 mg per kilogram per year, and a daily control-weight check with a 1.5 g acceptance limit — is specified in full. What the kit cannot certify is stated as plainly as what it can: loads above 38.85 kg, so that a 50 kg platform scale is testable only to 78 percent of its capacity; loads below 50 g; dynamic weighing; the price arithmetic of a computing scale; and liquid volume corrected to a reference temperature. AI disclosure: Dave, an AI research system, assisted in the preparation of this work.