Not all digitals suck
This is an old thread, but it appears that they are all old threads; so I thought I'd wake this one up.
Some analog hygrometers work well, some "close enough" and the majority (mostly cheapies bundled with humidors) are very erratic if they work at all.
Most of the digital hygrometers I've owned and used over the year (over a dozen, easily) are pretty accurate when properly used and maintained. "Maintenance" usually requires nothing more than replacing batteries when they start to go bad; a dying battery will definitely throw off the readings of most digital hygrometers.
I use Caliber IV "stick" hygros in my humidors; in fact, I just changed the batteries in four of them and they are undergoing the salt test to recalibrate them as I write this. While not every digital hygrometer has a means of adjusting the readout, the Caliber IV is adjustable over a range of +/- 6 percentage points, which is more than I have ever needed with one of them. In the morning I'll check their readings, adjust if necessary, and pop them back into my 'dors. (Although with Heartfelt 65% beads regulating humidity, I'm not sure the hygrometers are really necessary.)
I understand at one time Xikar marketed digital hygrometers that could be adjusted, but the newer ones lack that feature. Assuming the hygrometer works, and isn't off more than a few points with a fresh battery, just label it with a note reminding you of how many points you need to add or subtract from the readout, such as "+3" or "-1".
And if you have an analog hygrometer that works well, consider yourself very fortunate. Out of several that I have owned over the years, I have found just one that I consider usable; it's in the salt-test box with my Caliber IVs right now, and reading just one point low -- pretty good IMHO. (It's usually on my desk, rather than in a humidor; these days, the ambient RH in my home hovers around 35%.)
Incidentally, I calibrate my hygrometers twice: once at 75% using the normal salt test, and a second time using a 65% Boveda pack since 65% RH is what I actually prefer. Once my Caliber IVs have been adjusted to read true at 75, they stay within one point at 65; the one I had that didn't pass (it was three points low at 65) got tossed and replaced.