Accuracy of depth gauge

[DallasNewbie]

On our recent trip, my analog depth gauge always read shallower than my computer. In some cases it was off by as little as 5 feet, but on one dive, my computer showed a max depth of ~80' while the analog guage only went to ~65'. My computer was never more than 1' off when compared to my wife's (she doesn't have an analog gauge), so I'm pretty sure it's the gauge that was wrong. What's the acceptable error for these things, and should it be consistent?

 

[chrispete]

Are you asking whether the max depth should be off, or depth readings side-by-side. If the latter, you shouldn't have much difference (you will have as much as a 4-5' difference at 120' due to salt/fresh water because (most) computers can be set to salt/fresh while an analog guage cannot.)

I would bring the guage into your LDS for testing, they probably have a pressure vessel in which to test it...

 

[DallasNewbie]

Are you asking whether the max depth should be off, or depth readings side-by-side. If the latter, you shouldn't have much difference (you will have as much as a 4-5' difference at 120' due to salt/fresh water because (most) computers can be set to salt/fresh while an analog guage cannot.)

Both, I guess. I can see how the max depth could be off due to where the two instruments are situated, but that wouldn't account for a difference of almost 20'. According to the documentation for my computer it is calibrated for salt water, unless you are diving above a certain altitude.

 

[CIBDiving]

... but that wouldn't account for a difference of almost 20'.

Are you sure the analog gauge was 'zeroed' before the dive? There is an adjustment screw ( often in the side ) that lets you set the needle to zero, and I'm not talking about the max depth pointer. I'm not sure if that will account for all the error but it could be a lot of it.

 

[Toolbox-13]

Good point CIBDiving, deffinatly check that out and dive safe...:59:

 

[paolov]

have the analouge guage checked, it may be that corrosion is setting in hindering the movement of the needles axis.

On our recent trip, my analog depth gauge always read shallower than my computer. In some cases it was off by as little as 5 feet, but on one dive, my computer showed a max depth of ~80' while the analog guage only went to ~65'. My computer was never more than 1' off when compared to my wife's (she doesn't have an analog gauge), so I'm pretty sure it's the gauge that was wrong. What's the acceptable error for these things, and should it be consistent?

 

[DallasNewbie]

Are you sure the analog gauge was 'zeroed' before the dive? There is an adjustment screw ( often in the side ) that lets you set the needle to zero, and I'm not talking about the max depth pointer. I'm not sure if that will account for all the error but it could be a lot of it.

Is that something you are supposed to do before every dive? There are no screws visible when the gauge is mounted in the console, should I have to take it out to make this adjustment?

 

[BarryNL]

Both, I guess. I can see how the max depth could be off due to where the two instruments are situated, but that wouldn't account for a difference of almost 20'. According to the documentation for my computer it is calibrated for salt water, unless you are diving above a certain altitude.

True. The difference between salt and fresh water density is only about 2.5% so you would only see a difference of about 2' at a depth of 80' due to this.

 

[CIBDiving]

Is that something you are supposed to do before every dive? There are no screws visible when the gauge is mounted in the console, should I have to take it out to make this adjustment?

Well, you can take it out and see. Not all models may have it, I know at least some do, the model offered by Tusa does and Tusa doesn't build their own stuff ( recently they've sold a lot of Suunto products ).

You should *Check* the guage before every dive and be sure the needle is zeroed, Adjust if nessesary.

This is one of those things that computers do automaticly when they power up. I suspect that computer use may have made a few people forget how to operate anaolg guages

 

[DallasNewbie]

The gauge is an Aeries, and I just checked the manual online, and it doesn't say anything about an adjustment. I'll have to pull it out of the console when I get home and have a look. It definitely didn't read -20' at the surface, but I guess since the scale is logarithmic a small error on the surface will translate to a large error at depth.