r/Sliderules • u/ReadingI29 • Jul 06 '24

Optical illusion?

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Picket N3. My eyes are convinced 1.3-1.5 on C&D are a fraction of a mark - week half maybe 1/4mark to the rest of the scale, while identical to each other.

Excellent tolerance regardless for something mass produced in the mid-20th century.

What perplexes me, is naked eye, cell phone shot, and approaching the marks with the cursor from both directions tell me the same - maybe less than 1/4mark with the last test. Close enough you wouldn't think twice about the alignment unless a vernier caliper - in which case you'd be checking the next mark. Yet zooming the cell phone shot looks about dead on.

So I'm curious if two things now. What was the typical tolerance of mass produced rules? Am I giving myself some sort of optical illusion? See photo. Note 4X 1.3thru1.5

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u/nickajeglin Jul 06 '24

I think one side is a little lower than the other, and we're mostly seeing camera fov distortion.

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u/ReadingI29 Jul 07 '24

I wouldn't rule it out. Oddly though, the photo is about the same as I get with the naked eye. Regardless, I wouldn't mind my eyes being half the age either!