this post was submitted on 31 Mar 2024
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you're right. the person who initially brought up 9.5 was comparing it to the sae equivalent 3/8 (9.525mm, but whos counting).
the reply was what i was thinking of, the obvious answer: "what if you need to divide by 3?"
so good eye.
one scenario when i'd want a precision answer to 1/3 of 9.5 but also not have immediate access to a calculator is when woodworking. you know, seeing as how 9.5 is (the actual metric defender this time's approximation of) 3/8... and there's no way that a calculator would help me there because the result of 9.5/3 is 3.16, a length i'd need at least tenth millimeter vernier calipers to accurately scribe. even 9.525/3 is 3.175, a measurement that requires um precision to scribe!
the inch side of my ruler, however, is graduated in eighths of an inch and i can make that measurement easily with it.
i've also used a third measurement of a known diameter when drilling holes in metal to use a technique described in machinerys handbook to cut slots.
you were the one who asked what a third of an eighth was. i'm not sure why. why did you bring up a third of an eighth? was it because you thought it would allow a person to more easily answer the question what is 1/3 of 9.5?
i guess my real question is this:
how does a calculator help you make more accurate measurements?
using a ruler to measure a length of 1/8" is as accurate as using a ruler to measure a length of 31mm and eyeballing 2/3 of a mm
the bottleneck at that point is your eyeball and pencil lead, not the unit of measurement
well, it's 3.16 mm, not 31.6, but i get your meaning.
in that case if you wanted to be real precise, you'd measure from the left or right side of one graduation to the same side of the next graduation. using that technique a person could get a better 1/8" off a ruler than someone eyeballing fractional mms would.
I still don't see how a calculator helps though.
well yeah, because 1/8" is 3.175mm
1/3 of a mm is a distance between 1/64" and 1/128"
mechanical pencil lead is only about 0.4mm
don't ask me ask the person who posed the "what's a third of 9.5mm" question
Usually when I’m making a precise line, I’ll put an edge on the pencil lead so it will make a mark thinner than its diameter.
I seem to remember you as the one who brought up calculators, but I’m open to being mistaken.
even if you're in a situation where it's somehow possible to manually draw 1/3 of a mm to any accuracy, 1/3 scale draft rulers still exist for metric, so it's equivalent
because as soon as you have access to a calculator, "off the top of your head" is an irrelevance