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I feel really dumb asking this question, but I need help reading the lines on my tape measure. I need to make precise measurements, but given the thickness of the inch lines, I'm not sure how. I've added lines in the following picture.

enter image description here

I assume 1 inch is exactly the distance from the red line to the green line, or alternatively, the distance from the cyan line to the pink line. Is this accurate?

Ben A.
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2 Answers2

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That's the wrong tool for the job.

A carpenter's tape isn't intended to do better than about 1/32" (half the width of the smallest marked interval). Taking into account the sliding hook arrangement (which accounts for its thickness), the relatively imprecise bend in the hook, and the printing quality and you simply can't do what you seek to do.

But you be the judge.

enter image description here

To address your final question, your assumption would have to be correct or there'd be a cumulative error in the tape measure. Left-to-left, center-to-center, and right-to-right are all correct answers to a different question than what's in your title. You can select any point on the tape and the same relative point in the following inch demarcation and you'll have an inch. The implication here is that you can "cut an inch" (or any unit) and use only the lines rather than the hook, but it still comes down to your eye (and your math skills).

isherwood
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    If you want precise measurements with a tape measure it's often best to not use the hook, but rather hold the tape with the one-inch line aligned to the starting point, then add one inch to the measure you get on the other end. – Hot Licks Jul 12 '22 at 20:17
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    I agree most tape measures the “tab or hook” has more slop than the line with. ++ – Ed Beal Jul 12 '22 at 20:39
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    The "slop" should be the thickness of the tab. It is done that way so both inside and outside measurements are correct within the tolerance of the tape measure. – Gil Jul 12 '22 at 20:47
  • Yep, but it's still slop. Who knows how much debris or other inaccuracy is at play. – isherwood Jul 12 '22 at 21:04
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    @HotLicks — the phrase on my sites is “burn an inch”, but I prefer to burn 10 because math is hard and 28 could turn into 29 or 27 if you aren’t careful. – Aloysius Defenestrate Jul 13 '22 at 02:51
  • @Gil -- The "slop" is fine if you don't need exceedingly accurate measurements, but often the hook is not very precise. – Hot Licks Jul 13 '22 at 03:12
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    @HotLicks, _subtract_ one. A four-inch thing will go from the one inch line to the five inch line. – ilkkachu Jul 13 '22 at 07:04
  • Not to mention how thick the pencil line OP is going to draw! It's like when you measure 16" centres. You measure from right side to right side, (or left to left). Never centre to centre. – Tim Jul 13 '22 at 07:27
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    @ilkkachu - Yeah, I got that backwards. – Hot Licks Jul 13 '22 at 12:40
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    The hook is mostly for if you're measuring something that's long enough that you can't reach both ends of it at the same time, and you don't have a 2nd person to hold one end. The amount of potential slop it adds is usually not relevant at those scales. – Darrel Hoffman Jul 13 '22 at 14:49
  • I guess I was mistaken and you are using a cheep dimestore tape measure, I use professional quality tools. Try this link: https://www.popularmechanics.com/home/tools/how-to/a19950/the-simple-reason-why-a-tape-measure-hook-has-play-in-it/ – Gil Jul 13 '22 at 16:03
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    LOL. It's a Stanley, the industry standard around here, in 25' size. That doesn't change the fact that dirt can get in the slots and the rivets can loosen in the mylar blade over time. No need for sanctimony. – isherwood Jul 13 '22 at 16:05
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    As a side note, I tend to use the same tape to do all measuring for a project. For example, if I'm measuring a gap to fill with drywall or a 2x4, I measure the gap, then use the same tape to measure what I'm cutting so I can make sure that what I saw on the tape the first time is the same as when I go to make the cut. I also grew up on a farm where precision better than 1/8" was showing off. I've become a self taught DIY engineer and CAD designer where CNC routing and 3D printing means 15 thousandths can be make or break. I now have probably 3 different styles of calipers because of that. – computercarguy Jul 13 '22 at 16:33
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    @isherwood mylar? Isn't that a normal steel tape? Even cheapish ones have the right amount of slop when they're new to account for the thickness of the hook, but you're right that they age. – Chris H Jul 14 '22 at 09:28
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The rule of thumb I've always been taught is that the line width is the inherent uncertainty of the measuring device. For example, a nice, laser etched starrett rule allows you to quite positively slot the edge of a marking knife right into the measurement - to the uncertainty of the width of that slot. The line of a measuring tape is no thicker than a pencil line, which is generally the marking tool used in conjunction.

This is, unfortunately, not a hard and fast rule but a "trick of the trade", however it generally maintains itself as cheaper measuring tools generally have thicker lines.

Brydon Gibson
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