Driving home to altitude

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rsingler

Scuba Instructor, Tinkerer in Brass
Staff member
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Messages
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Location
Napa, California
# of dives
500 - 999
@Shearwater, in another thread,
Can anyone suggest a computer for returning to altitude after a dive
the question of driving home to altitude was raised. While I don't expect you to offer up an answer as to what's "safe", I'm hoping you can comment on the theory.

In surface mode, can I track GF99 over time? In other words, as my tissue map blooms in the last twenty feet of my dive, and I presumably surface with my planned SurGF or GFHi, my GF99 will begin to fall during my surface interval.

Will my Perdix then track altitude as I drive home? And will my GF99 show an increase if I jump in the car and start driving up the mountain? And can I display it in real time after my dive?

And finally, is my logic correct in thinking that if I keep my GF99 below whatever arbitrary value I've decided is safe, that using that to track risk of ascent after diving is valid? Note that I'm NOT suggesting using this to fly after diving, due to the sudden increase in cabin altitude, not to mention the risk of cabin decompression. Rather, I'm contemplating using this to help me get over the pass from my Lake Tahoe dive, and decide how long before I get in the car.
 
@rsingler do you have one of those vacuum bags that you can squeeze blankets and stuff in? or a vacuum sealer for food? You could stick the computer in one of those and apply a vacuum to it and see what it does
Actually, that's a great thought. I have a clear pressure vessel that I use for testing computers after service. There's no reason I can't remove the Schrader valve and do a little suction instead. I'll try it, thanks!

Wait. Your idea is better. I can't manipulate the buttons inside the container. I'll try and find a storage bag.
 
I tried my toy sucking air out with a syringe while displaying the tissue map and GF99, but can't get a reaction.
20200121_190102.jpg

I suspect I'm an order of magnitude short on air sucking ability using this method.

The tissue display and GF99 stay visible for quite awhile, but unfortunately the millibar display reverts to the standard screen after only a few seconds, so I can't see how much I'm reducing pressure with this method.

I might have better luck with a smaller container. More to follow, unless Shearwater pops in with an answer soon.
 
I think they suck all the air out but won't actually lower the pressure as the bag itself is flexible.

true, but I was thinking since the sensor is in a recess on the hard body, it would see some sort of vacuum. Doesn't have to be much, 1/2ATA is 16,000ft which is quite a lot of altitude change.
 
but unfortunately the millibar display reverts to the standard screen after only a few seconds, so I can't see how much I'm reducing pressure with this method.
.
The millibar display is part of my watch face in my Teric so it can stay as long as I wish, on my recent commercial flight I was wearing it on my hand and it was correctly displaying about 760 millibar which is correct approximate pressure inside the pressurized airliner and represents about 8000 ft in altitude. But I didn’t look unfortunately what GF99 was doing.
 
The millibar display is part of my watch face in my Teric so it can stay as long as I wish, on my recent commercial flight I was wearing it on my hand and it was correctly displaying about 760 millibar which is correct approximate pressure inside the pressurized airliner and represents about 8000 ft in altitude. But I didn’t look unfortunately what GF99 was doing.
Then your next task is clear. :D
Can't wait for your next plane ride!

Seriously, anyone reading this thread, wear your toy and watch your GF99 on your next plane ride. See if it goes up from 0 to anything greater...
 
I just did a test today using my backup camera housing. I have a vacuum pump to lower the pressure in the housing to check for leaks.

First I tested it with my Garmin Descent Mk1 which displays altitude. I live at around 270m although when I started the test the Garmin said 330m (I never said it was accurate :wink: ). Anyway, I sucked it to -10kPa and it said the altitude was 1200m which is more than 700m more than 330m.

Next I tried the Perdix. Now... I actually dived this morning and my surface interval was just shy of 4 hours when I tested. Before I started my GF99 was already at 0. I then sucked out -20kPa and the GF99 stayed at 0.

Here's my tissues graph around 10 minutes later:
PerdixTissues.jpg
 
https://www.shearwater.com/products/swift/

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