1.1K subscribers in the hypeurls community. OFFICIAL COMMUNITY OF HYPEURLS.COM: r/hypeurls is a Reddit community for sharing and discussing new tech… More on reddit.com

https://www.unitconverters.net/typography/millimeter-to-pixel-x.htm More on reddit.com

You can print out metric ruler templates in three sizes: 30 cm with 1 mm graduations, 3 x 15 cm with 1 mm graduations and a "meterstick": 3 templates which you cut out and stick together to make a 1-metre rule. Make sure you have the scale factor on your printer software set to 100%. I printed the 30 cm ruler as a test and found that: • There is a 1 mm gap in the bottom left and top right corners if you use A4 paper and Apple's Preview software to print out the PDF - Probably caused by the margin settings. • The accuracy is within 1 mm compared with an industrial-grade metal ruler with engraved markings. Edit: The NIST has a set of free classroom resources including metric rulers. More on reddit.com

This is incorrect. There is an accepted definition of an inch, and it is 25.4mm (1/36 of an international yard . The mm in turn is defined by the distance light travels in a vacuum in a certain amount of time as defined by the frequency of Cs-133 atoms. This seems difficult, but ultimately every measuring device gets its numbers from the above...it's just that your cheap ruler is likely a few iterations removed from the direct measurements I mentioned, with some small amount of error introduced from each iteration. Edit because of OPs edit: reference objects were exactly the problem years ago when definitions were tied to physical items such as a platinum iridium rod. With the current definitions, though, length is tied to universal constants that can be determined without worry of decay of the item. More on reddit.com