Should I go Full Metric from the Start ?

[stuartv]

Even if I dived with a computer that has Air Integration, I would use an independent SPG all the same.

The "If you need 1, then you need 2 " philosophy, I believe.

Well then, you have the answer to your problem. Use one SPG in Imperial and one SPG in Metric!

 

[Neilwood]

then why don't we use dual SPG's in normal recreational diving? If you dive AI I recommend keeping an analog gauge on the boat, but what are you doing that is so mission critical that an SPG failure or HP hose failure *VERY VERY common* wouldn't allow you to call the dive?

I think when wireless AI was introduced, there were widespread issues with transmitters/receivers dropping out which did make the a lot more problematic than the simple SPG so I can understand the historical position of rec & in particular tech divers to wireless AI.

In this age though, the rate of drop outs/faults is probably approaching that of SPGs so I would agree that it is now getting to the point at which it is SPG or AI but not both at the same time. I will be stripping mine and putting it in my gear bag as a spare (just need to check the SPG will be robust enough without the boot or buy a single boot for it - it is as per the link).

 

[TMHeimer]

Temp for those who really want to get it right is for F to C is subtract 32, multiply by 5 and divide by 9.

I have a simple way in my head for it though:
Take a temp in F - say 80F.
Subtract 32 = 48
Multiply by 5 = 240 (easy mental way is multiply by 10 and half it)
divide by 9 = 26.4C (divide by 10 and and a tenth of that back)

Makes the mental arithmetic a lot easier as instead of working out what 1/9 of 48 is.

Reverse is easy as well:
Take a temp in C say 30
multiply by 9 =270 (x10 less a tenth)
divide by 5 = 54 (divide by 10 and double it)
Add 32 = 86.

The only thing to really remember is which way the 32 goes (I tend to think of it by way of the alphabet and their place in it - C is lower than F so C<F is lower therefore subtract.)

Whoa--too much work for me. Memorizing "what =what" in the other thing seems easier (60F=16C and figure out what 63F is from that). But my wife always says I'm a "memorizer". I learned kilometers by looking at my speedometer which had both. Our latest car has a speedometer where you push a button to change from one to the other--that wouldn't have helped me at all.

 

[Roger Hobden]

an SPG failure or HP hose failure *VERY VERY common*

SPG failures and HP hose failures are very common ???

I had no idea.

 

[tbone1004]

SPG failures and HP hose failures are very common ???

I had no idea.

SPG failures are exceptionally rare, the only ones I have seen were the plastic ones failing catastrophically, and the good ones going WAY out of spec for accuracy

HP spool failures are VERY common, and I'll see a couple a year on my personal regs *granted there are 12 of them, but still*
HP hose failures are not uncommon, though I had 4 fail on my in the last year. They usually don't fail catastrophically they usually just look like an air stone in an aquarium, but it's still enough to call a dive.

With that, if I were to run AI, I would not put it on a HP hose, and I certainly wouldn't use a standalone SPG unless the dive was mission critical. I don't really know of anyone who does that, including the elite cave divers *of which I am not*.
The analog SPG introduced 2 extra o-rings with a high propensity to fail, as well as a hose which has a pretty high propensity to fail, all to be able to continue a dive in the event that you lose signal from the transmitter? That doesn't make any sense to me

 

[Roger Hobden]

Us new divers raising all these basic issues, I guess ...

 

[Kevrumbo]

Of course the math is easier in bar. But intuitively 40 bar just doesn't mean anything to me. Indeed, I do these sorts of mental shortcuts all the time so I can visualize it. @tbone1004 nailed it in his previous post by equating it to language. Unfortunately, I spent a lifetime thinking in the "language" of imperial units.

Alright fair enough, but also realize that context has a lot to do with understanding, assessing and giving meaning to a particular value. For example, 40 bar metric remaining and showing on a SPG means to me I better be at the surface and have just ended a dive.

I was certified OW and Advanced twenty years and did about 30 dives but then stopped diving. I am starting back again and have projects to do a GUE Fundamental Skills course very soon.

I downloaded the course materiel and started doing the gas management exercices. I have been doing a lot of supplementary reading also. Comparing the Metric and Imperial systems, it appears the Metric is much more simple and intuitive for all aspects of dive planning.

I am thinking of going Full Metric and for instance buying a SPG that reads in Bars instead of PSI.

I live in Montreal, Quebec, Canada, and I realize that probably most potential buddies around me will still be using the Imperial system.

Any thoughts and comments about me taking this route ?

Why Metric is more convenient both pre-dive and during the dive. . .

Gas pressure math is harder using more cumbersome US Imperial Units because of that extra superfluous digit in a PSI unit value:

In other words
-->which is the quicker much easier subtraction arithmetic to see & figure?

3000 minus 1160 equals 1840 PSI?

Or: 200 minus 80 equals 120 BAR???

All you need is a simple analog Bar SPG to confirm what you already figured and know in your head.

(Do you have a clue now @stuartv ?
If not, then you really ought to get two Perdix wireless AI units, one for each wrist, along with a redundant Data Mask and a NERD heads-up-display. . . all telling you what you need to know.)

 

[Roger Hobden]

Lol ! Do you guys talk to yourselves like that all the time ?

 

[Wookie]

I speak metric. I know that when the needle is in the red area, I need to be on the surface getting a fill. I know that if it's colder than 27 I need a wetsuit, and if I'm deeper than 40 Meters, I need to have a gas other than nitrox. Anything else is just details.

 

[RayfromTX]

Lol ! Do you guys talk to yourselves like that all the time ?

Only narcosis quiets the voices.