My new Perdix AI indicates 200 Bar. The SPG tells 210 Bar. How to know who’s right?
SPG or AI, Who’s Right?
- Thread starter Johanan
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
The Chairman
Chairman of the Board
If you surface with 50 bar, does it really matter?
However, my vote would be on the Shearwater.
However, my vote would be on the Shearwater.
DiverDownD3
Contributor
Try another SPG and see what you get seems like the easiest solution to me
OP
Normally I surface with at least with 100 bar from caves. ±10 bar influence calculations of thte turn pressure. But you're right. It makes the dive just slightly more conservative. It is about wanting your new gadgets working seamlessly.
Both my SPG's show the same...
The Chairman
Chairman of the Board
Most mechanical SPGs won't give you absolute pressure and are differential in nature. IOW, a greater ambient pressure results in a lower vessel pressure reading. Many electronic gauges are absolute in nature and calibrated to ignore that first atmosphere of pressure.
200 bar should be around mid-range where both kinds of sensors should be most accurate. I would check with at least another SPG, or better: another AI computer if you can find one. 10 bar out of 200 is 5%. Typical accuracy rating on pressure sensors is in 0.x% range so if the Perdix is wrong, it's very wrong.
Sean Walberg
Contributor
A man with one watch knows what time it is. A man with two watches is never sure.
Scared Silly
Contributor
You can not unless you have a calibrated master gauge. Just like you can not tell if a scale is correct unless you have standard (calibrated) weights.
That said the precision of an imperial analogue SPG is around 50 psi whereas for an imperial digital transducer SPG it is around 25 psi.
But remember a gauge maybe precise but not accurate. Accurate means is the value correct, precise means the values are repeatable. One can adjust for an inaccurate gauge but not an imprecise gauge. I.e. if a gauge always reads 100 units high just subtract that off. If a gauge reads a 100 units high, then 50 units low, then 50 high, it is not precise.
There is also resolution. Digital gauges are highly resolved but that does mean they are more accurate or precise than an analogue gauge. An analogue gauge with tick marks every 100 units means at best one can resolve the value to within 50 units.
That said the precision of an imperial analogue SPG is around 50 psi whereas for an imperial digital transducer SPG it is around 25 psi.
But remember a gauge maybe precise but not accurate. Accurate means is the value correct, precise means the values are repeatable. One can adjust for an inaccurate gauge but not an imprecise gauge. I.e. if a gauge always reads 100 units high just subtract that off. If a gauge reads a 100 units high, then 50 units low, then 50 high, it is not precise.
There is also resolution. Digital gauges are highly resolved but that does mean they are more accurate or precise than an analogue gauge. An analogue gauge with tick marks every 100 units means at best one can resolve the value to within 50 units.
Which is why 3 is the correct number to wear.
OP
Thanks for the good comments! I learned some new things about gauges and watches.
Similar threads
