Something that's bugged me about this notation though is that sometimes it means "cannot exceed the bounds" and sometimes it means "only exceeds the bounds 10% of the time"

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taneq 4 days ago | parent [-]

I don’t think I’ve ever seen mechanical drawings have “90% confidence” dimensions like this. If a part’s too big then it won’t fit, and it’s probably useless.

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kevin_thibedeau 4 days ago | parent | next [-]

If a test procedure is verifying all dimensional accuracy, it can be assumed to be bounding tolerance. If it's a mass production line with less than 100% testing of parts, you'd have to expect that some outliers get by and the tolerance is something like 3-sigma on a Gaussian.

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mabster 4 days ago | parent | prev [-]

Yeah it's probably field specific and I guess Gaussian-based uncertainty would be more about statistical sampling rather than tolerances. I've noticed that if arithmetic is being done on it it's almost certainly Gaussian. I just mean whenever I see uncertainty like this, I don't know what is meant!

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brabel 4 days ago | parent [-]

In Mechanical Engineering, tolerances ensure that when you put parts together, they will fit as long as the tolerances were respected.

It's not statistical. If the machinist makes a part that's not within the +/- bounds, they throw it away and start again. If you tried to fit multiple parts, all with only statistical respect for tolerances, you would run into trouble almost 100% of the time with just a few pieces.

	▲	mabster 4 days ago \| parent [-]
		Yeah understood. In electronics: Resistor values are Gaussian but they test and bucket the resistors so that they can be treated as tolerances for similar reasons.