Personally I don't use a hygrometer anymore. I'll explain in a moment.
When first starting out, I went with digital. Using the method that tapout described above, I calibrated the hygrometers (plural because I have four humidors). After a couple of years, I switched my humidification to RH beads. After using RH beads for about a year, I came to trust them and decided that I didn't need to use hygrometers.
Not sure how much effort and money you are planning on putting into this, but if money isn't an issue, you may really want to consider looking into the beads. Actually they are relatively inexpensive.
You can find them here:
www.heartfeltindustries.com or
www.cigarmony.com. And I think Cigarmony's direct link to their beads is
www.getthepuck.com.
I use "the Puck" in my three desk tops and heartfelt in my cabinet.
So the idea is that you buy the beads in the RH that you want. I prefer my cigars kept at 63-65 RH. I purchased 65rh beads. Now my hygrometers were already calibrated correctly. After a couple of years of using 65 beads and seeing my hygrometers constantly reading 64-65, I decided that the beads were indeed working and ditched the hygrometers all together.
I am an obsessive kind of person. Do a search on my posts from 6 or 7 years ago and you will find that I worried a lot about my humidity. Even when it was right, I still worried about my hygrometers. This hobby is supposed to be enjoyable and relaxing. The beads made the worry go away. They are foolproof and they work. I haven't checked my RH in a long time and my cigars smoke perfect. Well to my liking at any rate.
But to answer your question, don't use or rely on an analog hygrometer.
DL