Nightrider_1uk Thats why; as you know; all equipment have tolerances, usually based on percentages: Back in the day, when I was in Instrumentation, Standard Test Gauges (STG’s, for pressure) have an accuracy of +/- 0.25%, …..
The coffee roasters scales would also have an accuracy and would have to conform to weights and measures requirements. Over 1kg of coffee that could amount to 10g or more depending on the requirements of the law for selling off goods by weight.
Yes. It’s similar in weights and measures, but not quite the same. If I understand you correctly, the tolerance is linear across the range with pressure. It’s a similar principle in weights and measures but not quite linear. There’s a “Maximum Permissible Error” (MPE) usually measured in “e” which is a specific amount, for a given range of weight, but any given scale might have several of the bands within it’s range of measuring. i.e. maybe 0.5e for the first part of the range, 1.0e for the nex bit, and 1.5e for the last segment. The tolerances, therefore, aren’t a straight linear scale, but rather a sort of stepped linear, with plateaus.
In short, the principle, that the MPE is proportional to the magnitude of what’s being measured is the same, but the mechanics of the calculation are a bit different. And that’s why that same principle, MPE and the specific value of “e” at a given weight, allow the same legislation to apply to scales measuring pharmaceuticals in a lab, loose food products in a retailer. or a lorry in a weigh station.
In my case (at retailer/supermarket type weights) my calibration weights had to be regularly calibrated against (and by) local Trading Standards reference weights, which if I remember correctly, were calibrated against a UK “national” reference kilogram, which was calibrated against the overall world reference Kg, in Paris.
I should add I’ve been out of that game for years, and the above certainly relates to pre-Brexit. As the UK legislation was our implementation of prevailing EU law at that time, it MIGHT have changed, post-Brexit. I doubt it has, in any relevant way, and can’t see why it would, but I’m not current, so it’s certainly possible.
EDIT - It wasn’t just the weights that were tested for compliance, either. So were we. Company procedures had to be ISO9000, and individual testers (like me) were audited by visting Trading Standards guys to be sure we knew the laws, and followed them in implemention both calibration, and testing. Fun days. :D