# digital caliper calculator



## Ed T (Feb 24, 2010)

There's always a risk in these topics of revealing something that everyone already knows. I grew up with conventional measuring instruments (non-electronic). For the last 10 years or so I have been switching over to digital stuff because it seems a good value to me. For a large part of that time I used them the same way that I used the older technology. The trick here that's facilitated by the new technology is to use the digital caliper like a calculator. If you're working toward a dimension and you want to check how much more you have to go, simply set the caliper for the target dimension and zero it. Then measure your part and the display is a direct measurement of how far you have to go. No arithmetic involved. Maybe this is old news, but it was new and useful to me and maybe there's someone out there for whom it will be new and useful as well.


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## mklotz (Feb 24, 2010)

If you like caliper tricks, here's another one to add to your repertoire.

Center to center distance of two holes.

Put close fitting pins in the holes.

Using the calipers...

Measure across the outside of the pins.

Measure the inside distance between the pins.

Average the two measurements and you have your answer.

Note that the holes need not be the same size.


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## shred (Feb 24, 2010)

Yeah, I think the greatest asset of the digital calipers is not so much the quick reading (which is nice) but the ability to set zero wherever you want it.


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## thayer (Feb 24, 2010)

Here is another way to find center to center that is even easier if the pins are the same diameter. Measure one pin and zero the caliper with the pin in the jaws. Now extend the jaws to the outside of both pins. That will be the center to center distance.

Thayer


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## black85vette (Feb 24, 2010)

Not my idea so I take no credit. But to add several dimensions together:

1. move over .125 then hit zero button
2. move over .062 then hit zero button
3. move over .250 then hit zero button
4. close caliper and ignore the minus sign for your total


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## polepenhollow (Feb 27, 2010)

For converting Metric to decimal, Zero the caliper, select MM, open caliper to or measure desired piece in metric , press the MM/Inch button for an instant, very close conversion to decimal.
K Lively


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## IDP (May 14, 2010)

Or, If the pins are the same diameter zero the caliper on one of the pins and then measure across the diameter of both pins, the indicated measurement will be the distance between the hole centres.

Regards, IDP


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## Blogwitch (May 14, 2010)

One thing you haven't put into the equation is the overall inaccuracy of digital calipers. 
Two people will invariably get two different measurements when measuring the same dimension. 

Mainly tool flex, but also angles of measurement and general overall inaccuracy keeps them from being classed as a precision instrument, no matter how much it cost you. Some are more accurate than others, but that doesn't class them as being any better than an adjustable wrench to take the measurement then using an internal mic to take the reading off that.
Just holding them correctly can make a huge difference to the accuracy of the readings you can obtain from them.

They are for a quick check to 'near enough', not to exact and final size. For that you should be using more accurate measuring instruments.

That is of course dependent on how accurate you want to work to!!

Bogs


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## kf2qd (May 14, 2010)

As with all tools the accuracy depends on how the user handles them. Part of learning how to use any measuring tool is learning how to use it properly and accurately. Like the noob that uses the mics like a C-Clamp. Proper techniques will yield accurate repeatable results.

With calipers I pinch the outside of the jaws with my fingers when measuring an OD. No tendancy to bend them by trying to tighten them withthe thumbwheel. Not too hard to get 2 or 3 TENTHS of flex at ZERO with the thumbwheel.


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## Maryak (May 14, 2010)

Sorry Bogs,

But IMHO a good analog vernier caliper is just as accurate as a good analog micrometer, the latter being far easier to use. I have an inbuilt suspicion of digital readouts and having tried one such vernier, IMHO they upset the balance and feel. This vernier was given to me and has been relegated to the level of calipers where pretty close, (+/- 0.002"), is close enough.

kf2qd is spot on, it's a matter training and learning how to use the instrument(s) correctly.

If you can hit the size you require then the route taken is secondary but the cost of 8 micrometers versus one vernier caliper may convince you to practice with the vernier.

Best Regards
Bob


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## Blogwitch (May 14, 2010)

Bob,

If you noticed in my first line, I was on about digital verniers.

I use a mechanical clock vernier most of the time if I can't get a mic in, and even cheap ones will give a better reading than a digital one. They are usually good to guesstimating to 0.0005" (depending on the accuracy of the scale), but again, they must be used the correct way to obtain that reading. That is pressure from forefinger and thumb either side of the jaws, and as close to the measuring point as possible, with your other hand just supporting (not holding) the long arm, with the reading taken whilst in contact with the job, not locked up with the finger screw and read when withdrawn.

I did a very unenjoyable stint in a calibration dept of a metrology lab in a factory standards workshop, and came across almost every mechanical measuring instrument you could think of. 
The first thing we did with all calipers, it didn't matter whether mechanical or digital, personal or factory owned, we ground the internal measuring tips off because they were deemed just too inaccurate to be used, even when brand new.
Everyone in the factory had to submit their personal precision instruments for calibration if they wanted to use them in the factory, as using a non up to date calibrated instrument left them liable to severe disciplinary action.
This was just part of my job when working in a cleanroom factory making computer hard disk drives. In the workshops where they developed new drives, mostly from solid billets using manual machinery, measurement was a critical part of the manufacturing process.

So I got to use not only very expensive digital calipers, but the cheaper ranges as well. 

Not one of them gave me confidence enough to call them precision instruments, and were all marked up for 'not to be used for critical measurement'.

Maybe a bit too much info supplied, but it does show that digital verniers are not what most people expect of them.

I expect some of the very expensive ones have most probably come on a lot since I used to work with them, but the cheap and nasties should never be considered for critical measurement, you are just asking for trouble. I treat them as similar to a six inch rule. They are scattered about the shop, and picked up and used for when I want a near enough measurement. When they stop working, they are thrown away.

I bought a digital micrometer a while back, but haven't used it yet, I need to check it out using slips before I will consider putting it into action in the shop It reads to silly numbers of decimal points, but it is no use if it doesn't give the same reading each and every time.


Bogs


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## minerva (May 15, 2010)

> I use a mechanical clock vernier most of the time if I can't get a mic in, and even cheap ones will give a better reading than a digital one.




Bogs,
are you referring to the items listed here-

http://www.rdgtools.co.uk/acatalog/Vernier_Calipers.html
their Ref. Clock Vernier Caliper 0.001"
Ref: 76898

I have to date stuck with my old faithful analogue vernier for "accurate" dimensions but I noticed whilst reading the aero engine build frequent use of the dial vernier which seems a much more straightforward way to go for a relatively small capital outlay,if the items shown in the ad are they.

Hoping you can throw a little more light on the matter
TIA


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## mklotz (May 15, 2010)

Something that seems to go unmentioned in these calipers vs. micrometer discussions is the physical situation under which the measurement is made.

If one observes the (very proper) injunction to squeeze the caliper jaws carefully with the fingers, one ends up in a hopelessly contorted position trying to measure on the lathe. This awkward placement of body parts really increases the chance that the jaws will be inadvertently canted resulting in an oversize measurement. OTOH, a micrometer can be comfortably held in a position that yields an accurate measurement. 

Similar comments apply to many measurements made on the mill.

Measuring gage blocks while seated comfortably at the bench may show that calipers are really very accurate but that accuracy can easily be undermined when measuring in situ.


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## ieezitin (May 15, 2010)

Heres my two bobs worth.

Digital/mechanical instrumentation just does not work!. The marriage of two completely opposite system leads in inherently to inaccuracy and gross mistrust to the user.

Both have there place in the world but not together.

Accurate measuring is really an acquired skill that relies on observation, feel and patients. As its been said earlier holding the tool correctly while stance and body position all takes part in getting an answer to your read that will get you to your next step, notice that I said answer and not a firm measurement total.

My advice is use the best quality mechanical measuring equipment you can afford, get to know each piece well, the time invested in this will bring you trust, and trust is a paramount of importance. Always have one device for final close inspection and only use it for that purpose, use your junk stuff to get close. Take readings often and log on paper this forces you to pay attention to details and shows you what your machine is doing too plus its great for finding out where you screwed up!. Check re-check. After a while this gets to be second nature and your quality will improve.

I also do math in my head or on paper first then reach for the calculator for a second opinion. This keeps your gray nogging oiled, believe me now and again you need to use it.


Anthony.


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## Blogwitch (May 15, 2010)

Minerva,

The Clock Vernier Calipers are what I was on about. I have a Mitutoyo standard vernier from many years ago, but I now use a clock version because my eyesight is getting rather poor, and I can't see a standard vernier scale without using a loupe, which makes on the job measuring rather difficult. With a clock version, it is much easier. But if I can get a mic in, I will.

Both Marv and Anthony have raised very good points that need to be adhered to. 
I have dozens of mics that I have bought and had donated over the years, and have found that the cheapo Chinese ones do a very good job, as long as they are intially adjusted up and calibrated to your own sort of 'feel', which is what Anthony is on about. Now mine are set correctly for me, I have no trouble using them because the 'trust' is there.


Bogs


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## minerva (May 15, 2010)

Thanks John
I suspected as much and I can certainly identify with the mince pie probs. altho' thankfully I haven't reached the loupe stage quite yet except for checking the centre pop marks 
I think I will invest 12 squid and give one of the cheapos a try
regards 
terryT


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## Blogwitch (May 15, 2010)

I don't think you will regret it Terry.

I bought mine a couple of years ago, when my eyesight got worse (diabetes), from Arc Euro. I bought one metric 8" and one Imperial 8" for just under 7 squid apiece. They were getting rid of their mechanical stock at much reduced prices, and I haven't regretted buying them one bit.


John


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## doubletop (May 21, 2010)

Bogstandard  said:
			
		

> One thing you haven't put into the equation is the overall inaccuracy of digital calipers.
> Two people will invariably get two different measurements when measuring the same dimension.
> 
> Mainly tool flex, but also angles of measurement and general overall inaccuracy keeps them from being classed as a precision instrument, no matter how much it cost you. Some are more accurate than others, but that doesn't class them as being any better than an adjustable wrench to take the measurement then using an internal mic to take the reading off that.
> ...



I can see Johns point here and I suppose it depends how accurate you want the job to be. I can see the standards he sets himself, and being from a met lab that's going to be pretty high. My dad was a met lab man. As a kid I recall asking him to cut me some metal. "how long" he said, "an inch please". He'd get the hacksaw and randomly cut off a length for me and when I measure it it would be say 1.25". When I questioned it his reply would be that I hadn't specified the tolerance. Anyway he'd pick up the hacksaw again and cut another piece still without measuring it. That second one was exactly an inch long as far as I was capable of measuring it. He was capable of repeating that for as many lengths I required. OK they wouldn't have been exactly an inch but it was good enough for me. That lesson has always stuck with me, decide on the level of accuracy you require before you start and stick with it.

On the subject of the accuracy of digital calipers I ran my cheapo Chinese caliper past my slip gauges and it was spot on within the .0005 digit, so good enough for me. Yes I know I can get different readings depending how I use it so I always measure more than 3 times just to make sure I didn't get a bad reading on one of the attempts.

Pete


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## pete (May 30, 2010)

I really hope no one thinks I'm being picky. But as accuracy is being discussed here, When it comes to dial or digital calipers that's exactly what they are, Vernier doesn't belong in the same description of dial or digital calipers. A set of true vernier calipers has a vernier scale. Compared to a lot of people here I know very little but I did think this should be pointed out. I also realise that it's very comman for people to combine the terms and everyone knows what they are talking about.

I'd also agree that these tools are only approximate if your measurements need to be closer than + - .001 even for high end well built tools like Starrett or Mitutoyo. Cheaper calipers would no doubt have a even higher tolerance. My calipers are probably the most used tool in my shop but a person has to understand their limitations. For critical work they get me close, Then for say O.D. work the micrometers come out for a accurate measurement of how much more is to be removed. While I've never used a set of vernier calipers I have read that in well trained hands and with a very well made pair they can approach the same accuracy as a micrometer. To get that type of accuracy I'd imagine there would be some effort used to insulate the calipers from the heat in the users hands.

The inside jaws on dial or digital calipers are inaccurate but I still use them for fairly close measurements, Watch the dial or display on the calipers till you reach the maximum reading for an inside measurement, Lock the calipers, Then measure across the inside jaws with a micrometer. IMO this works pretty well.

Pete


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## Lew_Merrick_PE (Jun 2, 2010)

Not limited to digital calipers, but a trick I learned as an apprentice was to measure the overall length of my calipers and engrave that into a jaw. I can then use the ENTIRE caliper to make an inside measurement. Take the actual reading and add the overall length to it.


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## pete (Jun 2, 2010)

Lew,
Now that is a very clever idea, I have a project in mind that may take awhile to get to, But this idea is certainly far better than what I had planned for accurate, fairly large (+ 13") I.D. measurements for a shrink fit. 

Pete


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