Who needs an altimeter when you have a GPS? well, I just realized I can pair the two up and get barometric readings from the altimeter, and then, and THEN, maybe I can predict on-coming storms better.
After reading someone’s experience with a huge storm that rushed in during a long crossing, maybe a rapidly dropping barometer would have tipped them off…
Now if only I could get that TideTool program loaded into my GPS instead of my pda phone…
Oh and speaking of tons of batteries, good thing I carry spare CR2032 flat batteries for my headlamp, because my brother’s blood sugar meter ran out on a trip.
And after all that, I cook over a fire. Go figure.
But…
You can get a little analog barometer that doesn’t need batteries and is always on…
What will they think of next? 
gps alt
Is your gps alt reading accurate enough for your calculations? Mine is frequently way off, like 50% or more.
Also second on the dial alt versus a battery powered one.
Still, your idea of checking barometric pressure is a good one and can easily work this way - use a dial altimeter and 24K USGS maps, and the GPS to help fix your position on the map, then read your true altitude from the map and compare it to the altimeter.
Don’t need the gps
Unlees you are running steep whitewater you most likely will not change altitude much. Certainly not on big crossing. Use the altimeter as you barometer.
Thanks for mentioning the glucometer battery. Think I’ll pick up a spare!
Tommy
I have a TV mounted on the bow
which has the local weather shown every 10 minutes.
Trying to figure out barometric pressure was too complicated.
Paddlin’ on
G_K