## OT: imperial vs. metric units [Study Assessment]

Hi Angus,

» Yes; we are still in 1/16" units here. They are difficult to work with.

All scientific journals I know demand SI (

One story from my past: When I was already a diving instructor I went through my cave-diving courses in Mexico according to a US-system (NACD).

To calculate the maximum dive time (leaving air consumption for descent/ascent aside) in the metric system is bloody easy. Say the tank’s volume is 12 L and pressurized to 200 bar. The volume of expanded air is 12 × 200 = 2,400 L. If the breathing rate at the surface is 20 L/min, the tank’s air lasts for 2,400 / 20 = 120 min (ambient pressure 1 bar). If you dive, every 10 meters the pressure increases by 1 bar. Thus at 10 m the tank’s air will last for 2,400 / [20 × (1 + 1)] = 60 min, at 20 m for 2,400 / [20 × (1 + 2)] = 40 min, and so on. No pocket calculator needed.

How is this stuff done in the US? To start the confusion tanks are not classified by their volume, but by the volume of expanded air if the tank is filled to its rated pressure (which commonly is 3,000 psi). A standard tank is called “80 ft

In cave diving tanks are regularly “overfilled”,

» Yes; we are still in 1/16" units here. They are difficult to work with.

All scientific journals I know demand SI (

*i.e.*, metric) units. Imperial units are a mess.One story from my past: When I was already a diving instructor I went through my cave-diving courses in Mexico according to a US-system (NACD).

To calculate the maximum dive time (leaving air consumption for descent/ascent aside) in the metric system is bloody easy. Say the tank’s volume is 12 L and pressurized to 200 bar. The volume of expanded air is 12 × 200 = 2,400 L. If the breathing rate at the surface is 20 L/min, the tank’s air lasts for 2,400 / 20 = 120 min (ambient pressure 1 bar). If you dive, every 10 meters the pressure increases by 1 bar. Thus at 10 m the tank’s air will last for 2,400 / [20 × (1 + 1)] = 60 min, at 20 m for 2,400 / [20 × (1 + 2)] = 40 min, and so on. No pocket calculator needed.

How is this stuff done in the US? To start the confusion tanks are not classified by their volume, but by the volume of expanded air if the tank is filled to its rated pressure (which commonly is 3,000 psi). A standard tank is called “80 ft

^{3}”. A common “surface breathing rate” is 0.7 ft^{3}/min. The surface pressure is 14.5 psi and increases by 14.5 psi every additional 33 ft. Good luck in calculating the dive time.In cave diving tanks are regularly “overfilled”,

*e.g.*, to 3,333 psi. Then your 80 ft^{3}-tank contains 89 ft^{3}. There is also special equipment (compressors, regulators, pressure gauges) rated for 300 bar (~4,350 psi). In the metric system the 12 L-tank is still a 12 L-tank (what else). In the imperial system it’s a 116 ft^{3}-tank despite the dimension are the same. Crazy. I wonder why not more US-divers drown. Maybe they are better in math than me.—

Cheers,

Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. ☼

Science Quotes

Cheers,

Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. ☼

Science Quotes

### Complete thread:

- Dose Proportionality and Variance AngusMcLean 2016-05-11 16:55 [Study Assessment]
- More information, please Helmut 2016-05-12 14:34
- More information, please AngusMcLean 2016-05-13 16:40
- Setup in Phoenix/WinNonlin Helmut 2016-05-14 02:26
- Setup in Phoenix/WinNonlin AngusMcLean 2016-05-14 18:54
- Setup in Phoenix/WinNonlin Helmut 2016-05-15 14:47
- Setup in Phoenix/WinNonlin AngusMcLean 2016-05-15 15:17
- Phoenix 64 Warning Helmut 2016-05-15 15:56
- Phoenix 64 Warning AngusMcLean 2016-05-15 20:11
- OT: imperial vs. metric units Helmut 2016-05-16 16:26

- Phoenix 64 Warning AngusMcLean 2016-05-15 20:11
- Setup in Phoenix/WinNonlin ElMaestro 2016-05-15 20:54
- Setup in Phoenix/WinNonlin AngusMcLean 2016-05-15 22:30

- Phoenix 64 Warning Helmut 2016-05-15 15:56

- Setup in Phoenix/WinNonlin AngusMcLean 2016-05-15 15:17

- Setup in Phoenix/WinNonlin Helmut 2016-05-15 14:47
- Setup in Phoenix/WinNonlin AngusMcLean 2016-05-16 21:00
- NCSS vs. PHX/WNL vs. SAS Helmut 2016-05-17 01:50
- NCSS vs. PHX/WNL vs. SAS - Validation? mittyri 2016-05-18 08:23
- Diagnostics ElMaestro 2016-05-18 09:20
- Diagnostics: R and Phoenix Helmut 2016-05-18 15:14
- Diagnostics: R zizou 2016-05-22 19:07
- Diagnostics: R Helmut 2016-05-23 01:22
- SASian potpourri d_labes 2016-05-24 12:02
- Compilation Helmut 2016-05-24 14:27
- REML or not d_labes 2016-05-24 16:33
- complete or not Helmut 2016-05-24 16:57

- Compilation AngusMcLean 2016-05-26 16:46
- doubts about NCSS Helmut 2016-05-26 19:13
- Doubts about NCSS zizou 2016-05-26 23:38

- doubts about NCSS Helmut 2016-05-26 19:13
- Compilation AngusMcLean 2016-05-28 00:51
- Kenward-Roger? Helmut 2016-05-28 15:59

- 90% confidence interval for R_dnm Shuanghe 2019-01-04 17:45
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- Visualizing lmer and limits Shuanghe 2019-01-07 11:05
- Visualizing lmer and limits d_labes 2019-01-07 15:08
- Visualizing lmer and limits mittyri 2019-01-13 23:53

- 90% confidence interval for R_dnm Shuanghe 2019-01-07 10:53
- 90% confidence interval for R_dnm d_labes 2019-01-07 15:17
- 90% confidence interval for R_dnm Shuanghe 2019-01-07 17:11
- 90% confidence interval for R_dnm d_labes 2019-01-07 18:24
- offtop: greek letters and tables mittyri 2019-01-08 00:19
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- 90% confidence interval for R_dnm Shuanghe 2019-01-07 17:11

- 90% confidence interval for R_dnm d_labes 2019-01-07 15:17

- Visualizing lmer and limits mittyri 2019-01-06 17:00

- 90% confidence interval for R_dnm d_labes 2019-01-05 14:01

- REML or not d_labes 2016-05-24 16:33

- Compilation Helmut 2016-05-24 14:27

- SASian potpourri d_labes 2016-05-24 12:02

- Diagnostics: R Helmut 2016-05-23 01:22

- Diagnostics: R zizou 2016-05-22 19:07

- Diagnostics: R and Phoenix Helmut 2016-05-18 15:14
- Smith’s paper Helmut 2016-05-18 14:44
- Smith’s paper d_labes 2019-01-05 15:00

- Diagnostics ElMaestro 2016-05-18 09:20

- NCSS vs. PHX/WNL vs. SAS - Validation? mittyri 2016-05-18 08:23

- NCSS vs. PHX/WNL vs. SAS Helmut 2016-05-17 01:50

- Setup in Phoenix/WinNonlin AngusMcLean 2016-05-14 18:54

- Setup in Phoenix/WinNonlin Helmut 2016-05-14 02:26

- More information, please AngusMcLean 2016-05-13 16:40

- More information, please Helmut 2016-05-12 14:34