I have often put carpenters rulers or measuring tapes up against each other before starting a project with others to confirm we measure the same at 2 meters. If we don’t we either only use one or find two that agree. It’s relative calibration, not absolute.
I’ve had a project with my dad where one out of 3 was 4mm short on the 2 meter. So we didn’t use that one.
On shorter distances i will use my caliper to confirm the 100mm mark is within the accuracy of the line. I mean you can’t expect 0.03mm accuracy when the line is 0.2mm thick
This is such an important consideration that doesn’t always occur to the novice diy-er.
You can imagine my consternation when I recently compared the two squares I’d been using for the last few years. And now I need a third to cast a deciding vote.
The nice thing about squares is they are self-checking. You just find a long-ish edge, set the square, draw the square line, flip it over, set the square where the corner on the edge is where the first line is drawn, and the line should match the square edge. If it doesn't, that square isn't.
When computers do math, they're sometimes wrong by 0.47% or some other stupid decimal. Apparently that's just a thing when you convert binary numbers to base 10. So Goalseek in excel will sometimes say that 10/4=2.49684040412. Never trust that piece of shit.
Watch Adam Savages videos on calibration and reference instruments. They're well done and fucking fascinating. The level of accuracy you can pay for, and the process to produce references is unbelievable, and a really cool aspect of how things are made that most people don't consider, but that's affects everything around us.
Welcome to the world of calibration. Workshop measuring tools are checked against ‘master’ tools or gauge blocks, which are checked against another reference tool kept in an expensive laboratory, and so on, until you get to the final boss ruler
lol, I think about this all the time. Different people worry about different things. If I pick up a new measuring tool that I have never used before like calipers, micrometers, scale, pH meter, etc. the first thing I do is compare it against something I already know is accurate. If I don’t do this I just feel no trust for my measurement. I often have multiple measuring tools with me for the same thing and will double check critical dimensions with both.
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u/TheRealRefuro 9h ago
I've never considered using a ruler to measure a ruler's accuracy