What is it for?

[FirstBubba]

Without googling it I would have said "A really good compass".

There is still value in having such a really good compass once you learn how to use it. I have been navigating by GPS a lot since about the late 1980s but where you can't get a GPS signal or the overhead structure obscures your satellite signal, this compass would help. One example is in the Rocky Mountain wilderness where dense overhead forest cover blocks satellites or where your cell phone gets no communication signal. In a locale like that, I always carry a compass (not one that good) and have used it to find my way back to camp several times. In many wilderness locales, cell signals just don't exist for apps like maps and navigation.

Last time I went to Kodiak fishing, the guide headed out to a GPS location on his boat. There was NO signal. When I asked how far out we were, he just smiled and said, "You're in international waters!" and laughed. We were like +/-20 miles off shore. The rock fish bite was fantastic. That is the only time I've been out of sight of land when fishing Kodiak.
Here in south Texas, there are two spots we frequent where there is no cell phone signal.