SPG accuracy question

[Jake]

Earlier this year I bought a SPG from Deep Six but never used it. I acquired a Perdix AI a few months ago, and last week my wife got her own Perdix AI.

I wanted to check her Perdix against mine before diving it and thought I’d use the Deep Six gauge as well.

On a full HP steel, both Perdixes showed identical pressure at about 3600, whereas the SPG showed about 3900.

I then put them all on a pony I have which I know to be about half empty. The Perdixes were again identical and read about 1350, whereas the Deep Six registered about 1425.

This freaked me out a bit so I checked another analog SPG and it confirmed the Perdixes. I also tried different HP ports just in case.

I’m surprised to find an analog SPG that’s so far off, so I’m wondering if there’s something I’m missing. Does this sound like something that could be caused by a bad HP hose or connection point or anything else?

Thanks in advance.

 

[chris kippax]

The SPG may become more accurate as it gets to the lower end of the scale. Test it out on your next dive.

 

[decompression]

Spg’s are generally around 200-300 PSI off........

 

[Tortuga68]

What's important is that the SPG needle hits the stop before the tank is empty. Full and half-full are only indicative

 

[dmaziuk]

Bourdon tubes respond non-linearly. SPGs would be calibrated to be most accurate at the middle of their range, but metal fatigue will change that with age.

 

[Fin Finder]

I own several SPGs.
I like diving the one that gives me the most air.

 

[Charles2]

Perdixes showed identical pressure at about 3600, whereas the SPG showed about 3900.....The Perdixes were again identical and read about 1350, whereas the Deep Six registered about 1425.

I would declare this amount of error to be unacceptable, especially in a new gauge. Suggest that you return the gauge to @cerich at Deep6. Even if it has been a while, It would be hard to believe that he won't make it good.

 

[lowflyer]

I would declare this amount of error to be unacceptable, especially in a new gauge. Suggest that you return the gauge to @cerich at Deep6. Even if it has been a while, It would be hard to believe that he won't make it good.

I agree with this because I have a Perdix AI and a Deep 6 SPG, and they are in very close agreement.

 

[JamesBon92007]

If it gets hard to breathe when the needle hits about 140 psi then it's probably very close.

As for other accuracies, while doing a safety stop with my new computer the danged thing would have to update but with a depth gauge it's constantly moving so for me it's easier to see if I'm maintaining my correct depth. I have to wonder if the depth gauge or the computer is correct on the depth when they don't agree.

 

[dmaziuk]

I have to wonder if the depth gauge or the computer is correct on the depth when they don't agree.

Is your depth gauge set to EN13319?