reasonable depth gauge tolerances

[jhspb]

I just got my versa pro back from service. The depth readings from 33 to 140' were consistently low by roughly 7 feet. Is this reasonable? or not? Didn't ask the lds because I didn't notice til i was home.

Joe

 

[DFC5343]

Plus or minus a foot is the most. If your doing a decompression stop do you want to be off 7 feet? Bends case. Type one maybe even a two for 2-3 stops.

 

[DA Aquamaster]

Most current dive computers call for accuracy of plus or minus 1%. You should be getting accuracy to plus or minus 1 foot at 100 feet (and up to plus or minus 4 feet at 399 ft.)

If whatever you were comparing it too was accurate, your computer is screwed and needs to go back in.

Large scale errors across the board (7 ft off from 33' to 140') in particular are unusual and are more alarming than a small error that becomes progressively larger at depth (1 ft at 50', 2' at 100, 3' at 150 ft, etc. ) The last computer I had that had a large and consistent error died on the next dive.

Deco stops aside, your computer is also figuring your N2 loading for an entire dive either 7 feet too shallow or 7 feet too deep. To deep you could live with, but that much too shallow will get you bent.

 

[DFC5343]

A adjustable depth gauge is a must. I use a Princeton. Expensive but very accurate and can be adjusted for the situation. Just a thought.

 

[DA Aquamaster]

Good point and the accuracy of an adjustable gauge can be very important for accurate deco stops and in high altitude situations.

In the "old" days, capillary depth gauges were popular with deco divers as they were self adjusting for barometirc pressure and altitude and were quite accurate above 60 ft and very accurate and very sensitive from about 30 ft to the surface - ideal for accurately monitoring and maintaining deco stop depths.

 

[padiscubapro]

jhspb once bubbled...
I just got my versa pro back from service. The depth readings from 33 to 140' were consistently low by roughly 7 feet. Is this reasonable? or not? Didn't ask the lds because I didn't notice til i was home.

Joe

for that shallow a depth its a bit much.. 1 ft accuracy like some profess is not necessarily a given..

for example a guage calibrated for fresh water, will read 103 in salt water (1ft deeper per ATM)

The error you are detailing sounds more of an altitude compensation error.. I am unfamiliar with that computer, does it have an altitude mode?? Is it automatic??

For example I dive an explorer computer, when set in altitude mode, I can be at 16fsw actual depth but the computer only reads 10 fsw.. As long as I follow the deco stops using the dept as indicated by the computer everything is fine... If I use another guage, Id actually be violation my deco ceiling because the computer wants me at 10m of water pressure not actual depth.

 

[chrpai]

jhspb once bubbled...
I just got my versa pro back from service. The depth readings from 33 to 140' were consistently low by roughly 7 feet. Is this reasonable? or not? Didn't ask the lds because I didn't notice til i was home.

Joe

I always compare my depth gauge and computer during a dive. If they disagree I ask to see my buddies depth gauge. Which ever one his agrees with I trust.

And this has happened... I was in Jamaica and a rental gauge was reading 10' shallow. I told the DM at the end of the dive but I doubt they did anything about it.

 

[jhspb]

Thanks for the insights.

This is much more helpful than my LDS which told me that tolerances of were acceptable 10%.... even before you all commented I was struggling with this view ...but the N2 loading comment above sealed my reluctance to accept a view that a 10% tolerance was ok.

I assume that FO2 is also inaccurately measured with depth errors in the 7-10% range?