I'm a measurement geek. I spent the bulk of my career as a Metrologist. Metrology is the science of weights and measures. I have calibrated and repaired hundreds, if not thousands, of dial, digital and vernier calipers. So, get comfortable because I'm gonna give a primer on measurement tools.
First of all, a micrometer is much preferable to a caliper. They are more consistent and repeatable. The problem is a micrometer only has one function where a caliper has three. They can be had in outside, inside and depth versions. So, you'd have to buy three tools. Thus the caliper is preferable for common usage. We'll talk about accuracy later. That's all I'm gonna say about that.
Calipers come in three versions; dial, digital and vernier. I would steer clear of the vernier variety. It's really easy, even for a pro, to read them incorrectly. Also, most vernier calipers only have two functions; inside and outside. Vernier scales usually cost less, depending on brand and quality, but there are too many decent dial and digital calipers to worry about that.
Dial Calipers-
These are great. No batteries to worry about. Generally easy to read, but takes a little thought. You have to use the scale on the bar in conjunction with the dial. Not complicated, but I have seen mistakes made. The biggest problem with these is a little thing called backlash. Backlash is basically the slop that exists in the gears. If the gears had no slop, they would be so tight they couldn't move. So, even the most expensive dial calipers have some backlash to deal with. When using a dial caliper, always go one way. When taking an outside measurement, bring the jaws together in one smooth motion. This is not always possible. Some times you have to wiggle the caliper a little to be sure you're flat on the surface being measured. This is why all dial calipers have a tolerance of +/-1 division. That usually translates to +/-.001", but some are +/-.002" though I haven't seen one of those in a long time. I have seen dial calipers with better tolerances, but they are really expensive and digital is much more practical for that tight of tolerances.
Digital Calipers-
Digital calipers are much easier to use. There's only one thing to read and it's digital so, the number is what it is. Of course it sucks when you want to make a measurement and the batteries are dead. This has happened to me on more than one occasion and it's very frustrating. However, another benefit of a digital is the backlash is almost eliminated. Because of the way they work, backlash is no longer a concern, but hysteresis is an issue. Hysteresis is the slop (for want of a better word) of the electronics. The benefit is that hysteresis is easier to control and thereby reduce. Most digital calipers on the market today have a readout to .0005". The last digit is only a half digit. This means that it reads either a 5 or a 0. This is similar to reading the needle on the dial when it falls between hash marks. Not surprisingly, even the digital calipers have a tolerance of +/-.001". There are some that are much better than that, but break out the check book if you want one of those and they have to be handled in laboratory type environments.
In all the calipers I've calibrated in my whole career, I've noticed that both the dial and digital deliver the same repeatability and accuracy for general use. The digital is just easier to use. Also, I've calibrated Starrett, Brown & Sharpe, Mitutoyo and several other brands to include el cheapo Chinese stuff. All of them work fine as long as they meet certain criteria.
When you pick up a new set of dial calipers, close the jaws and hold them up to the light. There should be no light visible through the mating surfaces at all. Any light that comes through is cause for rejection. If there's no light, the jaws are parallel and that's what you want/need.
Now, that only checks the outside measurement jaws. Unfortunately, that's all you can check without some special tools or processes. With the jaws closed, look closely at the inside measurement jaws. There shouldn't be any light here either, but it's not as precise a test as the outside jaws.
The depth measurement is nothing that needs to be checked at purchase. If the other two jaws are OK, then the depth will work fine. The trick is how to zero the tool to use it for depth. All of them, even the most expensive, must be zeroed on a flat surface prior to making a depth measurement. Just closing the jaws and pressing zero won't work for depth and your measurement will be off by about .001" or more.
Now to brand. It has been my experience that Mitutoyo is the best when it comes to consistency. Over the years I've had the best results from them. But, and this is a big one, I'm really splitting hairs by saying that. All of them have delivered good quality. The "better" part of Mitutoyo falls in the realm of .00005" and none of us on this forum need that kind of precision.
I personally have three; dial and two digitals. One of my digitals is a left hand type. All of mine are the el cheapo variety and I've calibrated them and they are all within tolerance. As long as the jaws are parallel, I see no reason for a layman to spend $100 on a dial/digital caliper. If you can get a Mitutoyo or B&S, or are just willing to spend the cash, by all means do it, but you don't have to.
I'll rest here. I've given enough to read if indeed anyone has read this far. If anyone really wants it, I can post some pics (maybe a video) on how to use them properly.
At this stage in life I prefer the digital because the numbers are big, getting old sucks.
