ATJ
Contributor
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Gas Time Remaining.GTR?
GTR Mode
Gas Time Remaining (GTR) is the time in minutes that can be spent at the current depth and SAC rate until a direct ascent to the surface at a rate of 33 feet/min (10 m/min) would result in surfacing with the reserve pressure. The SAC rate is averaged over the last two minutes of diving for calculating GTR.
GTR can only be based on one tank. The Surface Air Consumption (SAC) measurements are also based on the tank selected for GTR calculations.
GTR on my Teric is not very accurate at the start of a dive. My Oceanic VT3 is quite accurate over more than 1500 dives. The Teric is better toward the end of the dive. No idea what the explanation is.I love the compass on my Perdix and I use it regularly.
I have two shore dive sites where I use the compass immediately after descending to get me where I want to be as quickly as possible. It gets me there perfectly (or within a few metres) every time.
I also love the AI on my Perdix. I have my Perdix mounted on my camera rig immediately above the viewfinder which literally makes it a "heads up display". It is easy to glance at it while taking photographs or while swimming. Having the Perdix mounted there also makes using the compass easier and more accurate - no bending of my arm and holding it steady to get a reading.
The only thing I don't like about the AI on my Perdix is the accuracy of the GTR especially earlier in the dive. It is ridiculously conservative - I don't know if this is by design or that they aren't taking the compressibility of gas into consideration. It gets more accurate as the dive progresses. I also carry an Oceanic and it pretty much nails it for the whole dive.
Yeah, we've had this discussion before. I still think that Oceanic consider the compression of gasses better.GTR on my Teric is not very accurate at the start of a dive. My Oceanic VT3 is quite accurate over more than 1500 dives. The Teric is better toward the end of the dive. No idea what the explanation is.
Does knowing your gas volumes to ten decimal places add any value? Unless you’re a Vulcan of course ;-)Now, I typically use a 300bar tank. Using the data from Subsurface, @300bar I have 3,197L of gas, @270bar it is 2,945L., @80bar it is 967L and @60 it is 717L. So the first 30 bar I use at the start of the dive is around the same amount of gas as the last 20bar. i.e. the SAC will appear to be higher at the start of the dive due to the differential compression of gas. In this example, it is 50% higher, which explains the SAC of 1.5 and the shorter GTR.
Quite.Does knowing your gas volumes to ten decimal places add any value?