I recently learned something scary about GPS. Don't just turn it on and believe the position it shows. It may have been a tech glitch, but I think it is something that commonly happens. Could be very serious on the water.
I've been learning celestial navigation at home. After quite a bit of study I did my first sun sights with my new sextant, land based, mid morning and mid afternoon shots. I'm far enough north that at that time (Christmas) the sun was very low, not the best for accuracy. I figured being a newbie if I could place myself in New England rather than Africa I'd be pretty happy. I then did my sight reductions and plotted my position.
I decided to check just how close I was to my actual position by putting my GPS where I'd taken the sights and turning it on. I left it for a bit to boot up and acquire 7 or 8 satellites. When I tried to get latitude and longitude I couldn't find it in the menu, just the chart (map here on land) and the speed and direction screens that I normally use.
After quite awhile (I'll estimate 15 minutes from turn on to numbers) I found the hidden menu and wrote down the exact latitude and longitude, then went inside and plotted it on the same plotting sheet as my sextant location (two LOPS crossing).
I was pleased to find I was only a few miles off. Just out of curiosity I googled my latitude and longitude, then plotted google's numbers on the same sheet. I was only 1/2 mile off!!!
I'd forgotten I'd left the GPS out there. Two hours later I saw it and the numbers had changed. It now agreed with google.
My sextant gave me a more exact location than my GPS!!! I attribute this to it taking time for the GPS to continually check and average readings from all the satellites. Or maybe just a glitch somewhere in the tech chain.
Perhaps it is well known that your GPS must be on for a long time to be accurate, but I did not know that. I thought when it gave an answer it was correct. I have now learned that GPS will always
give you an exact
location, even if it is wrong! Thinking about our aging satellites, our poor economy reducing our ability to upgrade them in a timely fashion, radiation and solar storms, computer glitches, etc. I intend to be even less certain about GPS positioning. Not to mention EMP weapons and cyber hacking. I've read that the Navy is going back to teaching celestial navigation because you can't hack the moon and stars.
I'm now inspired to go beyond being a celestial nav "trained monkey" and get a deeper understanding which will help with greater accuracy. Doing a land sight is inherently more accurate than bouncing around in a small boat. However, even a trained monkey can do quite well, and it is quite interesting and excellent exercise for one's brain. My own brain felt rusty and moribund when I started, but yes, an old dog can learn new tricks.