Gerry's advice above is excellent.
I supposedly have three of these things, all relatively inexpensive.
I have managed to lose the one with the largest display, and it was also the most reliable, consistent and accurate (Tchibo). I am now stuck with either one that occasionally skips measurements when moving the jaw (but doesn't seem to be inaccurate), or one from Lidl which is completely unreliable at small values.
So I'm heading in the direction of Moore & Wright, DML or even Mitutoyo, as I use them a lot. Ideally I'd like one that will do fractional inches too, but those don't seem available to similar quality. If you look at the reviews, you find comments that reflect my experience. And realistically there isn't going to be much QC applied to something as cheap as these usually are. Plan (A)is Amazon, but I might go to Axminster, as their service is so good.
There is no magic in this: I have a Gem Red angle box which is pretty rubbish, as was one of their hinged rules (for angles - threw it away as quite untrustworthy). I now have one of the latter that does work properly. It seems to be a lottery, and expensive doesn't seem to mean accurate or reliable, apart from the big brands.
If you're lucky and get a good one, they're brilliant, but I won't go to Lidl for that sort of thing again, as being untrustworthy (in measurements) is worse than anything else. Being able to take it back for a refund is small compensation after you've messed up something because it lied to you.
Custard's idea of a mechanical, dial one, is also under consideration, as that is straightforward too.
I'll settle for poor precision, but not errors in repeatability or accuracy.
DML from Amazon is favourite at the moment.