Should I go Full Metric from the Start ?

[tbone1004]

@kelemvor I never said the math for PSI was easier, I said that psi is easier for most people in the US to work with. Huge difference. If you are used to a unit, and can THINK in a unit, using another unit is more difficult. It also means in the US having less accurate gas volumes because most of our tanks don't actually list the water capacity of the tank so you have to start in the cf/psi value and then convert to metric for all of your tanks to work in liters.

In terms of accuracy, going to tenths of a degree in celcius is more accurate than fahrenheit which is only normally given in full degrees, and giving tenths of meters is more accurate than ft which is normally given in full units as well.

 

[beester]

I don't know about .001m but I can definitely maintain buoyancy without bouncing around 3' (1 meter). Same with the temperature measurement; look back at my post. To get any level of precision in the ranges I'm used to in metric your only option is to use fractions/decimals to some degree. I don't know about "in blue water". That doesn't seem relevant to my point. I can still count on one finger the time I've had to hold a stop or other depth without a visual reference point. I guess if those are the dives you do, then maybe maintaining tight buoyancy control might be something you have to loosen up on.

It's not that difficult to feel a change in water temperature when moving from 72f to 73f water.

In the end, it doesn't matter other than to illustrate part of the reason I'd be uncomfortable switching to metric for distance or temperature when diving. YMMV.

I don't think you understand my point. It's that it's totally irrelevant that you can hold a stop to 0.33m (1 foot) of baseline it doesn't mean anything. I think I'm doing my share of blue water no reference ascends. Some even quite deep (60-90m range (200-300ft))... and I'm very accurate in my buoyancy, but in real life scenarios keeping your depth within a 1 m range is more than sufficient for all diving scenarios even with very significant deco obligation. If you think you'll get a deco hit if you are 1 foot shallower or deeper then you are dillusional.

Explain to me when you would need in water accuracy up to 1 foot in ascend profiles?

Same with water temperature. Yes of course you will feel a difference in temperature if you hit a thermocline. But normally that difference in temperature would be in the 2-3 (sometimes even 8 to 10) degrees celcius range. Not in 0.1 degrees

 

[Kevrumbo]

. . .I never said the math for PSI was easier, I said that psi is easier for most people in the US to work with. Huge difference. If you are used to a unit, and can THINK in a unit, using another unit is more difficult. . .

For base reference and derived units of pressure, what's easier and more intuitive to work with?

Multiple factors of 14.7 psi which itself is equivalent to 1 atm (1 ATA) ?
-->Or multiples of 1 atm (1 ATA) which itself is approx 1 bar of pressure?

Also, it's easier to do the equivalent arithmetic with two significant figures in bar pressure units versus three sig figs in psi: Again, what is easier to SEE and THINK in your head -->

200 minus 80 equals 120 bar ?
-or-
3000 minus 1160 equals 1840 psi ???

The motivation to use Bar Metric in Scuba is to work smarter -not harder. The extra digit in arithmetic with PSI units actually makes it harder and less intuitive to work with, and the reason why divers (like @stuartv) who use US Imperial may need the extra expense of a computer with Air Integration, Air Time Remaining & other digital logging features, versus a simple analog Bar SPG with understanding practical manual arithmetic using the Metric System.

. . .It also means in the US having less accurate gas volumes because most of our tanks don't actually list the water capacity of the tank so you have to start in the cf/psi value and then convert to metric for all of your tanks to work in liters. . .

The common AL80 tank has a metric cylinder rating factor of 11 liters/bar (look it up online if unfamiliar, for any particular tank), or in other words, at the surface of 1 bar, if you pour water into the cylinder, the measured volume it can contain is 11 liters. (It's easier to work with Metric Cylinder Ratings like 11L/bar, rather than cf/psi like 0.025 cf/psi for the AL80 tank)

However when pressurized to any value up to its recommended Service Rating (207 bar for the AL80 tank/11L per bar cylinder in this example ), a cylinder carries an equivalent volume of free gas much greater than its water capacity, because the gas is compressed to several hundred times atmospheric pressure (while water is incompressible). So if you have a gas pressure reading of 200 bar in your AL80 tank, you have a total available free gas volume of 200 bar times 11 liters/bar or 2200 liters.

. . .In terms of accuracy, going to tenths of a degree in celcius is more accurate than fahrenheit which is only normally given in full degrees, and giving tenths of meters is more accurate than ft. . .

In Scuba, the cardinal reference numbers for depth in meters goes by three's: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30 etc ---->while in US Imperial Feet, the equivalent depths goes by ten's: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 etc. (Notice that simply by inspection, you can determine depth in ATA from the Metric sequence easier by dividing-by ten and adding one, versus dividing-by 33 and adding 1 in the US Imperial Feet sequence).

For non-computer Dive Table purposes, accuracy in either unit system doesn't really matter since by convention and conservatism, you always round to the next deeper depth for those values falling in between the reference cardinal numbers (i.g. 7 meters rounds to 9 meters; 25 feet rounds to 30 feet).

Finally for degrees Celsius, it's all "qualitative", and so "accuracy" or precision within the average habitable ambient air temperature range of 20°C to 25°C is moot, because of other factors such as wind chill, relative humidity, precipitation etc. You use the appropriate exposure protection that's most comfortable (sweater, jacket, rain poncho etc). Similarly for Scuba water temperature in that same range, with factors such as thermocline depth, level of physical activity and total time of dive & exposure to consider, you may need a 3, 5 or 7mm wetsuit with or without hood. Any variation above this range 20°C to 25°C, you're looking in general at a skinsuit to board shorts and a rash guard; any temperature below this range and drysuits become the exposure suit option. . .