If you were given a choice between dial, digital and vernier calipers which one should you pick?
When I went looking for a caliper I wanted a dial type, based on the following comment in Andy Rae's book Choosing & Using Hand Tools, "A plastic dial caliper is plenty accurate for a woodworker's needs, and costs peanuts compared to more expensive metal versions."
I couldn't find one for sale locally, in plastic or metal, and eventually got a digital model in stainless steel. I did eventually spot a dial caliper but it was more expensive, and it turns out I wouldn't have been as happy with it — Rae is clearly right that they're more than accurate enough for woodworking, however, after using the digital type I wouldn't recommend one on a couple of grounds.
As far as woodworking in concerned what would make one preferential over the other or is this just a matter of personal preference?
Potentially slow to read (requires interpretation/calculation by the user, which can introduce error) but in practice for the woodworker this is arguably irrelevant as the accuracy is beyond what's usually achievable in wood.
Can be very expensive, but oddly the plastic versions appear to be the cheapest calipers available (less than the price of a cup of fancy coffee).
Can have both metric and Imperial scales on the one tool.
Very simple mechanically, so little to go wrong.
No batteries required so will work anywhere, any time, without fail.
Accurate enough for woodworking needs.
Where available, can be cheaper than digital.
Display is often harder to read than on a digital model, but note: the opposite in bright sunlight.
Dial mechanism can be knocked out of alignment or break entirely, rendering the dial readout useless (no user-serviceable parts inside).
Almost all are either Imperial or metric, not both.
No batteries required.
Normally easier to read. Especially important as your eyesight diminishes getting older! But, possibly important to some users, the typical LCD display is difficult or impossible to read in direct sunlight or bright daylight.
Instant read, so faster to use (particularly when compared to vernier calipers).
More accurate than dial or vernier, sort of. Disregard what you hear to the contrary, they are more accurate in practice than dial calipers; this isn't to do with the build accuracy or better machining of the gearing, it's simply a by-product of the digital display of the measurement (to two or three, sometimes even four decimal places).
Re-zero function at any opening size allows easier comparison measurements (both positive and negative) of e.g. a mortise and its corresponding tenon, two similar drill bits, a jig's pin with the matching router bit.
Can be expensive, but careful shopping will pay dividends here — buy directly from China and you can get what appears to be exactly the same tool as a name-brand version, just without the logo and the resulting mark-up!
Particularly important feature I feel: metric and Imperial on the one tool; and this can be changed on the fly.
Requires batteries for the digital readout. But, they still retain the basic marked scales that a vernier caliper has, and the housing for the digital display is deliberately sized do that you can use its edge to read the measure:
So for 'rough' measurements they will still give service if the battery has died. I say 'rough' here as of course it's no rougher than the measurements done with a conventional rule, which we rely on as accurate all the time.