Question Any objective data on SPG or transmitter failure rates?

[BoltSnap]

Good point. I tend to forget about the ones that I (almost) never see in the wild...

You aren't wild enough. You need to get out of your shell more often.

 

[arkstorm]

@arkstorm Unfortunately, a poll on SB would be subject to selection bias and recall bias and not give me objective unbiased data. I'm sure it would be interesting, however.

I respectfully disagree.

The selection bias would be offset by the factor that you are measuring failure per number of dives. In analyzing the data you would probably need to establish a minimum number of dives for data to be counted because, e.g., a very unlucky diver may have only had relatively few dives with a failure which would likely skew the results compared to the median number of dives per failure. But the sample group as a whole could be within reasonable tolerances.

Also, SPG/transmitter failure has no relation to the level of experience or enthusiasm of a diver, i.e., one that is more or less likely to be a scubaboard member, let alone one who would reply to a poll. I would agree with the contention that your average scubaboard member has more dives under the belt than the average diver but using respondents from this population is reasonable to represent scuba divers writ large when the data is per total number of dives as opposed to per diver.

Recall bias is always a problem in every poll but does not necessarily render it un-objective. An SPG/transmitter failure is likely not something a diver would either forget or falsely remember because what we know coming into the matter is that it does not happen often. Recall bias is managed by properly setting forth the poll question and defining the operative terms.

To maximize validity, I would pose the poll as follows:

1) How many dives have you completed in your lifetime (approximately)?

2) How many times has an SPG (tank pressure gauge connected by a hose) failed to provide you with your tank pressure after entering the water for a dive but before exiting the water?

3) How many times has a transmitter (tank pressure gauge connected wirelessly to a display device) failed to provide you with your tank pressure after entering the water for a dive but before exiting the water?

I would compile the data as such:

(a) I would eliminate responses from divers with less than 100 lifetime dives.

(b) I would apply a bell curve concept to define a median reported failure rate.

(c) I would define a margin of error based on the number of reports which fell outside the median.

(d) I would consider how many total reports (N=?) I would require to identify a statistically significant determination.

I believe that with enough responses the results of such a poll would be a valid indicator of failure rates over a large sample number of total dives.

I would not share my prediction/thesis prior to the poll to not bias the results.

Would be an interesting exercise if nothing else.

 

[Wants2divemore]

All good points, and upon further reflection, I do think you're correct about selection bias and recall bias probably not being significant in this case.

 

[arkstorm]

Edit:

I would add to questions 2 and 3 the phrase, “…for the remainder of the dive…” to eliminate failures reported due to transmitter signal being lost momentarily but then being reestablished during the dive.

 

[esmIII]

You also need to consider that the average age of SPGs on people's gear is likely older than the age of transmitters. Furthermore, do you consider a battery dying on a dive a failure? Or is it user error. What about a hp spool with a slight leak? What if a computer dies underwater? Do you count that?

 

[Seaweed Doc]

I've never had an SPG failure. I can't even recall a leak around the spool, though I've noticed that on rental gear others were using all the time. My ancient SPG is likely off a bit, but not enough to concern me.

If by transmitter failure, you mean "Seaweed is an idiot," , then yes, I've had transmitter failures. When I first used one, I didn't realize that any temporary disruption of transmission had to be acknowledged even though transmission was solid after a brief disruption. Acknowledge it, and you're seeing remaining air. I should have studied the manual more....

Then there's the "oops, forgot to change the battery in the transmitter or receiver" error that I find under water.

Never had either issue with an SPG.

YMMV.

 

[Whitrzac]

I instantly disregard anyone who says they've never had an spg fail.

I have less than 100 dives using standard spgs rather than transmitters(400+ dives) and have had 3 spgs fail. One had read 500psi at 0. One the gauge face came off and would rotate, the other read 4000 at 3000psi.

I've had 0 transmitter failures.

I don't count button gauge failures, they're consumable items at this point, I keep 2 in my save a trip kit.

 

[arkstorm]

You also need to consider that the average age of SPGs on people's gear is likely older than the age of transmitters. Furthermore, do you consider a battery dying on a dive a failure? Or is it user error. What about a hp spool with a slight leak? What if a computer dies underwater? Do you count that?

I would propose to define a failure as any situation which caused the diver to be unable to ascertain their remaining tank pressure for the remainder of the dive. I realize that would include computer failure if using a transmitter but that is ok because that is one of the failure points when using hoseless ai.

 

[stuartv]

I would propose to define a failure as any situation which caused the diver to be unable to ascertain their remaining tank pressure for the remainder of the dive. I realize that would include computer failure if using a transmitter but that is ok because that is one of the failure points when using hoseless ai.

I don't think that's entirely fair. For MOST recreational scuba divers, the computer failure would mean their dive is over, whether they are using an SPG or AI, so it shouldn't count against AI but not count against SPG.

The outliers are ones who actually dive with 2 computers and could/would continue their dive even after one computer died. And that is further complicated by the possibly that the backup computer has or does not have AI.

I have 2 AI computers. I dive with both a lot of the time. If one computer dies, my other will still tell me my cylinder pressure and I would have no reason to end a recreational/NDL dive at that point. If it was a technical/deco dive, then yes, one computer dying means end of dive. But, again, that is the case whether I'm using an SPG or AI.

 

[Belzelbub]

That is a terrible feature.

Exactly. Makes no sense. I can understand alerting if the connection is lost, but to require intervention to display after connection is restored is useless. The log should record that the COMMS were lost at various points, so you’d be able to see if something was causing interference.

I’m going to guess Suunto.