Easy Way to Round "Big" Fractions from Digital Calipers - Woodworking Talk - Woodworkers Forum
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post #1 of 32 Old 02-21-2018, 05:51 PM Thread Starter
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Easy Way to Round "Big" Fractions from Digital Calipers

I saw this thread...

http://www.woodworkingtalk.com/f2/calipers-194881/

... and it got me thinking about how to solve a minor annoyance with digital calipers:

I have an iGaging IP54 Electronic Digital Caliper. I like it very much. The one drawback is the way that it displays fractions. If your measurement rounds to 128ths, you see 128ths. You can't set it to round to the nearest 1/16, for example.

I have some small experience with math, but rounding quickly from 128ths is not my best skill. Sometimes I want to round the reading to what I think is the "real" or "intended" value, and not the exact measure. That's because I may accidentally tilt the caliper jaws when measuring, for example.

When I see "113/128" on the caliper display, I am not super fast at figuring out that the "actual value" or "rounded value" is 7/8 inch. It turns out that 113/128 is only 1/128th of an inch above 7/8 inch. The actual value is probably 7/8ths, but I angled the caliper jaws when I made the measurement.

To deal with that, I just made a quick and dirty spreadsheet in Excel. When you get a "large fraction", use the table in the spreadsheet to scan for a nearby row with a "longer line" to round up or down to a "nicer" fraction in 16ths, 8ths, or whatever.

INSTRUCTIONS:
At the top of the chart, find the denominator (bottom) of your fraction on the caliper display. Slide your finger down the column until you find the numerator (top) of your fraction. Now look just above and just below it for a row that has more values to the right. You must decide how much you want to round up or down. (How far away from your reading that you want to stray.) It depends on whether you are looking for the nearest 16ths or 8ths or whatever, to get your "rounded" value.

The next time I go out to the garage, I will tape this printout inside one of the cabinets. I hope it helps others.
Attached Files
File Type: pdf Fractions Table for Digital Calipers.pdf (24.9 KB, 94 views)

Last edited by Tool Agnostic; 02-21-2018 at 05:53 PM.
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post #2 of 32 Old 02-21-2018, 06:08 PM
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simple math

It's taken quite a while, but over the years I've memorized some decimals from fractions. 1/4" = .250, 1/8" = .125, 1/16" =.0625 and so forth. You can get to all the others by adding those fractions together:
5/16" is 1/4" plus 1/16" so .250 + .062 = .312 etc..... no need to memorize them all, just the basic ones.

Going backwards from digital (decimals) to fractions means subtracting the big easy ones like .750 0r .500 and dealing with the remainders. Here's a good chart if this doesn't work for Ya:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #3 of 32 Old 02-21-2018, 06:10 PM
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Might have to get a calculator and covert it to decimals. 113/128 comes out to .8828125 which is a fuzz over 7/8". It's less than 1/64" so I would round it to 7/8". Unless you are figuring the openings of a number of shelf spacings there is no reason to get into 64ths in woodworking.
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post #4 of 32 Old 02-21-2018, 06:53 PM Thread Starter
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Quote:
Originally Posted by Steve Neul View Post
Might have to get a calculator and covert it to decimals. 113/128 comes out to .8828125 which is a fuzz over 7/8". It's less than 1/64" so I would round it to 7/8". Unless you are figuring the openings of a number of shelf spacings there is no reason to get into 64ths in woodworking.
Thanks. Your decimal method works well. I would want something like your chart, but out to 128ths, since that is what the digital calipers display.

For now, I'll give my home-brew chart a try first; I think it will be the fastest solution for me.
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post #5 of 32 Old 02-21-2018, 07:03 PM
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I have a drill graph similar to @woodnthings does drill size, fraction and decimal the 3 I usually need
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post #6 of 32 Old 02-21-2018, 07:12 PM
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Quote:
Originally Posted by Tool Agnostic View Post
Thanks. Your decimal method works well. I would want something like your chart, but out to 128ths, since that is what the digital calipers display.

For now, I'll give my home-brew chart a try first; I think it will be the fastest solution for me.
I don't know, I've never seen a tape measure with 128ths increments. The dimension wouldn't mean anything unless it translates into usable increments. You might be better off with a caliper which reads in decimal equivalencies. If you use it enough it doesn't take long to memorize the decimal equivalencies of at least the 1/16" increments on the tape measure. The decimal equivalence is then rounded off to a usable dimension.
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post #7 of 32 Old 02-21-2018, 07:32 PM
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I've never seen a tape measure that read to better than 1/16." I have a precision Starret scale that reads to 1/64" on one side and 1/100" on the other. My Wixey digital readout on my router table reads to 1/64, but I ignore everything beyond 1/32"

Someplace in my youth, I was require to memorize the decimal to fractional equivalents table to 1/64" and have never forgotten it. So my decimal-only dial calipers reads 1/1000's, and I still calculate in my mind to 1/64"

YMMV

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post #8 of 32 Old 02-21-2018, 07:33 PM
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I do so love a good millimeter. so simple . . .
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post #9 of 32 Old 02-21-2018, 09:16 PM
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The best way I know to handle a problem like that is to get rid of the offending caliper and buy one that reads the way you want it to read.

George
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post #10 of 32 Old 02-22-2018, 07:12 AM
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Guys the problem was solved in 1791 when the Metric system came into use.
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Measure twice, Cut once, Then force it to fit with a big hammer.
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post #11 of 32 Old 02-22-2018, 07:13 AM
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Quote:
Originally Posted by GeorgeC View Post
The best way I know to handle a problem like that is to get rid of the offending caliper and buy one that reads METRIC the way you want it to read.

George
Fixed that for you
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Measure twice, Cut once, Then force it to fit with a big hammer.
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post #12 of 32 Old 02-23-2018, 01:19 PM
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Most of time when using a caliper it's to transfer a measurement and I don't need to turn it on for that. If measuring to 1/8 or 1/16 then a rule should be good enough. I actually prefer working in tenths of an inch.
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post #13 of 32 Old 02-23-2018, 02:35 PM
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I don't know why the calipers won't let you set the degree of accuracy you want. 32nds for imperial and 1/2 millimeters for metric would be plenty for me in most cases.
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post #14 of 32 Old 02-24-2018, 06:09 AM
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Quote:
Originally Posted by quickstep View Post
i don't know why the calipers won't let you set the degree of accuracy you want. 32nds for imperial and 1/2 millimeters for metric would be plenty for me in most cases.
cost/price!!!
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post #15 of 32 Old 02-24-2018, 11:31 AM
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I printed this one up and have it in the shop.
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post #16 of 32 Old 02-24-2018, 12:44 PM
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Quote:
Originally Posted by Quickstep View Post
I don't know why the calipers won't let you set the degree of accuracy you want. 32nds for imperial and 1/2 millimeters for metric would be plenty for me in most cases.
You can buy fractional dial calipers. Also those pocket calipers measure in fractions and metric.
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post #17 of 32 Old 02-24-2018, 01:02 PM
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Stick to the metric system. Common global language.

For dead stuff, wood moves.
You cannot measure it with any accuracy.
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post #18 of 32 Old 04-04-2020, 04:00 PM Thread Starter
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I just got a PM asking for better instructions on how to use my "Fractions Table for Digital Calipers.pdf" chart. Let's see if this makes it easier:

Instructions:
1. Print the chart and put it in a place where it is handy. Mine is taped on the inside of a cabinet door.
2. Get a reading from the caliper in fractions of an inch (not decimal inches or mm).
3. Look at the bottom part of the fraction, the "denominator" - 128, 64, 32, 16, 8, 4, or 2
4. Put your finger on the top of the column with the matching denominator.
5. Slide your finger down the column (or the second column) until you see the top part of the fraction, the "numerator."
6. Look above and below your finger for a "nearby" fraction with a longer row. The longer nearby row may extend out to the 16ths column or the 8ths column or perhaps the 4ths column.
7. Use the nearby line that you found in step 6 as a close estimate. Read the number for the numerator (top) of the fraction.

EXAMPLE:
Your caliper reads "41/64":
* Take your finger and put it on the top of the "64" column in the second half of the chart.
* Slide your finger down the 64ths column until you reach the "41".
* Look two rows above it, and you will see a longer line "80 - 40 - 20 - 10 - 5" Note that the "5" is in the "8ths" column.
* Your 41/64 inch measurement is slightly larger than 5/8 inch.

Your measurement is only 2/128 inch larger than 5/8 inch, so perhaps the intended measurement was supposed to be 5/8 inch.

I hope this helps.

Last edited by John Smith_inFL; 04-05-2020 at 07:33 AM. Reason: per OP request
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post #19 of 32 Old 04-04-2020, 04:31 PM
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Quote:
Originally Posted by Quickstep View Post
I don't know why the calipers won't let you set the degree of accuracy you want. 32nds for imperial and 1/2 millimeters for metric would be plenty for me in most cases.
Calipers are made to be accurate, just get some old fashioned ones with the marks on them where you can see how close you are to those 32nds.

Wise men speak because they have something to say; fools because they have to say something -Plato

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post #20 of 32 Old 04-04-2020, 05:59 PM
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A couple of things here. . . .

Back in the early 1970's, when we tried to convert to the metric system, the stay at home Moms in the US said "I won't cook in metric". For those of you who don't understand, cooking in metric is by mass and not volume.

The rest of us, that are mostly borderline inept in the kitchen decided to remain imperial rather than starve.

Also, there is a company that makes digital displays. Terribly expensive for a table saw (several hundred dollars) and a really bad customer service but solved the problem. I don't know if it is patented or not. After the fraction there are three bars. You configure the display for 1/16 or 1/32. Then the fraction is displayed plus the number of bars over the faction. If you see 11/16 plus one bar, the measurement is 23/32 or 11/16 plus 2 bar is 47/64. The nice thing is that you know about where you are.

Harbor Freight sells a batteryless caliper for about $3. It will read to the nearest 1/128. However you can read w/o a problem and w/o counting to a 32 just by a quick glance.
https://www.harborfreight.com/hand-t...per-63664.html
Occasionally they are on sale for $1.
The bad thing about the caliper is the numbers wear off easily. I spray them with clear Krylon before putting them into use. I have compared their measurements to a couple of digital calipers. They are all right on. The batteries in your digital calipers will wear out 3 or 4 times before you'll wear the numbers off of one of these. When you buy them just make sure that they read zero when closed.

For those of you of the Metric persuasion, the caliper will read to tenths.

Rich
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