Yea, I'm always blown away by the old master machinists I've worked with when they talk about getting to "50 millionths" (ie half a tenth of a thou) on manual l

Yea, I'm always blown away by the old master machinists I've worked with when they talk about getting to "50 millionths" (ie half a tenth of a thou) on manual lathe and measurable with a bench micrometer [1]. Also the auto body guys whose hands are like profilometers [2] and can just feel various surface quality [3]. This is actually where precision originally came from with the 3 plate lap where you're just using fingers and candle soot to create crazy high surface flatness [4]. [1] https://willrich.com/product/starrett-direct-reading-bench-micrometers/ https://willrich.com/product/starrett-direct-reading-bench-m... [2] https://en.wikipedia.org/wiki/Profilometer https://en.wikipedia.org/wiki/Profilometer [3] https://en.wikipedia.org/wiki/Surface_roughness https://en.wikipedia.org/wiki/Surface_roughness [4] https://ericweinhoffer.com/blog/2017/7/30/the-whitworth-three-plates-method https://ericweinhoffer.com/blog/2017/7/30/the-whitworth-thre...