Checking depth gauges

[diverdon]

I suspected some discrepancies in my depth gauges so I thought I'd check to see which worked and which didn't. I knew of at least one that didn't work but now I know there are 2. Shore diving in Mqt is shallow diving unless your prepared to go for a nice long swim and that wasn't happening today. I hope to repeat this test next weekend at Crystal Falls where there is plenty of depth and its easy to get to In the meantime check out the differences. I'll update this later when I can test them at a deeper depth.














To be continued...

[duckbill]

Reminds me of the time I took a bag full of all my gauges out to 50 feet in Monterey Bay. I wrote on a slate what each read, and logged them in my PC for reference. They were mostly good to +/- 3'. but the worst one was off by 7'. Don't forget that if you are at any altitude the capillary gauges will not (or should not) jive with the bourdon gauges.

[SeaRat]

I have a set of correction factors for depth gauges at altitude. I put these on a Concise Weights and Measures Conversion Tables and Circular Slide Rule I have from the 1970s. I still have it, sitting in front of me right now. These came from talks by Dr. Bell in the 1970s about diving at altitude.


Note that the Capillary Gauge corrects in favor of safety, giving the diver using it a safety factor (if not the true depth--it reads deep). In this case, if the capillary gauge reads 55 feet, the actual depth at altitude is 50.7 feet at 3000 feet altitude. Similarly, if I dive it Clear Lake, at about 5000 feet altitude to 60 feet on the gauge, the actual depth is about 51 feet. Using this depth on the decompression tables gives a safety factor.

The Bourden tube depth gauge reads shallow. If at 5000 feet, you need to add 4 feet to the reading. So if the gauge reads 60 feet, add 4 feet so that it's 64 feet depth. There is also a 3% correction for being in fresh water, which needs to be added. Adding the two factors will give a correct depth to a gauge that is in calibration of 60 + 4 + 1.8 = 65.8 feet, or 70 feet actual depth on the decompression table. This, obviously, puts you in a different category on the decompression tables.

This is also why it is very important when diving at altitude in fresh water to set up the dive computer to calculate at altitude/fresh water. I think all the new dive computers can be set up this way, but divers may not realize the need. This could get divers in trouble in, say Lake Tahoe diving.

'Hope this helps.

John

PS, do you see how much easier it is to read the simply analog needle/dial system than the digital number system at a glance. This has to do with perception ergonomics, and is a real potential problem with the new dive computers, especially for deep diving where narcosis can occur.