fixed setpoint EAD formula

**wedivebc** · 29th May 2007, 06:18

I was watching Leon teach a meg class recently and he wrote a real slick formula for calculating EAD using fixed setpoint. I tried to work it out on my own but can't come up with the algebra. Anyone care to help me?

almity1 · 29th May 2007, 06:38

Funny, I was reading about this today

Mastering Rebreathers Chapter 6 P152 (if you have it)

I do not know if this how Leon presented it.

almity1 · 29th May 2007, 07:19

Here is the formula.

Hope it is correct and it helps

**nigelh** · 29th May 2007, 09:07

If you're lazy and using the 'depth in bar' trick it is simply:
(depth - set_point)/0.79

dantheman · 29th May 2007, 13:06

Quote: (Originally Posted by nigelh)

(depth - set_point)/0.79

Not "accurate", but quite good enough for something like EAD.

--dan

**nigelh** · 29th May 2007, 14:14

Quote: (Originally Posted by dantheman)

Not "accurate", but quite good enough for something like EAD.

<sigh>Read the post.

brinoz · 29th May 2007, 15:11

Quote: (Originally Posted by almity1)

Here is the formula.

Hope it is correct and it helps

Ambient pressure = P = (D+10)/10 or = D/10 + 1 bar (+1 is the atmospheric pressure)
P N2 = P - PO2 bar

Equivalent air pressure = P eq air = PN2 / 0.79

Equivalement air depth = (P eq air - 1 )*10 m (-1 is the atmospheric pressure)

Personnaly, it makes no sense to know by heart such a formula, it is much easy to recalculate step by step.

Regards
Bruno

**wedivebc** · 29th May 2007, 16:02

Quote: (Originally Posted by dantheman)

Not "accurate", but quite good enough for something like EAD.

--dan

Could you explain to a math retard why that is not accurate?

**UWSojourner** · 29th May 2007, 16:34

Quote: (Originally Posted by wedivebc)

Could you explain to a math retard why that is not accurate?

Hey Dave,

Probably depends on what you mean by accurate. Maybe precise would be a better word.

The first formula is equivalent to
EADInBar = ( DepthInBar + 1 - PO2 ) / 0.79 -1

The "lazy" formula is
LazyEAD = ( DepthInBar - PO2 ) / 0.79

Now it's easier to see the difference. It boils down to this

Difference = 1 - 1/ 0.79 = -0.2658

The difference will be -0.2658 bar no matter what your depth or PO2. That's about 3 msw or 9 fsw. Seems pretty good to me, unless you're worried about your EAD at 6 msw

.

**wedivebc** · 29th May 2007, 20:07

Quote: (Originally Posted by UWSojourner)

Hey Dave,

Probably depends on what you mean by accurate. Maybe precise would be a better word.

The first formula is equivalent to
EADInBar = ( DepthInBar + 1 - PO2 ) / 0.79 -1

The "lazy" formula is
LazyEAD = ( DepthInBar - PO2 ) / 0.79

Now it's easier to see the difference. It boils down to this

Difference = 1 - 1/ 0.79 = -0.2658

The difference will be -0.2658 bar no matter what your depth or PO2. That's about 3 msw or 9 fsw. Seems pretty good to me, unless you're worried about your EAD at 6 msw

.

OK I am running numbers through almity's and nigel's formulae and coming up with the same result. What am I missing?

29th May 2007, 06:18	#1 (permalink)
wedivebc Dave Tomblin Current Rebreather/s: Megalodon Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Other CCR Join Date: Feb 2005 Location: Vancouver Island BC Canada Posts: 1,508	fixed setpoint EAD formula I was watching Leon teach a meg class recently and he wrote a real slick formula for calculating EAD using fixed setpoint. I tried to work it out on my own but can't come up with the algebra. Anyone care to help me? __________________ Cheers, Dave.... Man is the only animal burdened with the knowledge he will eventually die
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29th May 2007, 06:38	#2 (permalink)
almity1 No Viz is BAD Viz Current Rebreather/s: Megalodon Other Rebreather/s: Evolution Prism Topaz Sport Kiss Optima Join Date: Aug 2006 Location: Sydney, Australia Posts: 175	Re: fixed setpoint EAD formula Funny, I was reading about this today Mastering Rebreathers Chapter 6 P152 (if you have it) I do not know if this how Leon presented it. __________________ Cheers almity1 - http://www.almity1.com
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29th May 2007, 09:07	#4 (permalink)
nigelh New member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 883	Re: fixed setpoint EAD formula If you're lazy and using the 'depth in bar' trick it is simply: (depth - set_point)/0.79 __________________ nigelh
(Online)

29th May 2007, 13:06	#5 (permalink)
dantheman Emoticonoclast Current Rebreather/s: Sport Kiss rEvo Other Rebreather/s: Classic Kiss rEvo Join Date: May 2005 Location: NorthEast USA Posts: 397	Re: fixed setpoint EAD formula Quote: (Originally Posted by nigelh) (depth - set_point)/0.79 Not "accurate", but quite good enough for something like EAD. --dan
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29th May 2007, 14:14	#6 (permalink)
nigelh New member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 883	Re: fixed setpoint EAD formula Quote: (Originally Posted by dantheman) Not "accurate", but quite good enough for something like EAD. <sigh>Read the post. __________________ nigelh
(Online)

29th May 2007, 15:11	#7 (permalink)
brinoz RBW Member Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Sep 2006 Location: Belgium Posts: 55	Re: fixed setpoint EAD formula Quote: (Originally Posted by almity1) Here is the formula. Hope it is correct and it helps Ambient pressure = P = (D+10)/10 or = D/10 + 1 bar (+1 is the atmospheric pressure) P N2 = P - PO2 bar Equivalent air pressure = P eq air = PN2 / 0.79 Equivalement air depth = (P eq air - 1 )*10 m (-1 is the atmospheric pressure) Personnaly, it makes no sense to know by heart such a formula, it is much easy to recalculate step by step. Regards Bruno
(Online)

29th May 2007, 16:02	#8 (permalink)
wedivebc Dave Tomblin Current Rebreather/s: Megalodon Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Other CCR Join Date: Feb 2005 Location: Vancouver Island BC Canada Posts: 1,508	Re: fixed setpoint EAD formula Quote: (Originally Posted by dantheman) Not "accurate", but quite good enough for something like EAD. --dan Could you explain to a math retard why that is not accurate? __________________ Cheers, Dave.... Man is the only animal burdened with the knowledge he will eventually die
(Offline)

29th May 2007, 16:34	#9 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 558	Re: fixed setpoint EAD formula Quote: (Originally Posted by wedivebc) Could you explain to a math retard why that is not accurate? Hey Dave, Probably depends on what you mean by accurate. Maybe precise would be a better word. The first formula is equivalent to EADInBar = ( DepthInBar + 1 - PO2 ) / 0.79 -1 The "lazy" formula is LazyEAD = ( DepthInBar - PO2 ) / 0.79 Now it's easier to see the difference. It boils down to this Difference = 1 - 1/ 0.79 = -0.2658 The difference will be -0.2658 bar no matter what your depth or PO2. That's about 3 msw or 9 fsw. Seems pretty good to me, unless you're worried about your EAD at 6 msw .
(Offline)

29th May 2007, 20:07	#10 (permalink)
wedivebc Dave Tomblin Current Rebreather/s: Megalodon Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Other CCR Join Date: Feb 2005 Location: Vancouver Island BC Canada Posts: 1,508	Re: fixed setpoint EAD formula Quote: (Originally Posted by UWSojourner) Hey Dave, Probably depends on what you mean by accurate. Maybe precise would be a better word. The first formula is equivalent to EADInBar = ( DepthInBar + 1 - PO2 ) / 0.79 -1 The "lazy" formula is LazyEAD = ( DepthInBar - PO2 ) / 0.79 Now it's easier to see the difference. It boils down to this Difference = 1 - 1/ 0.79 = -0.2658 The difference will be -0.2658 bar no matter what your depth or PO2. That's about 3 msw or 9 fsw. Seems pretty good to me, unless you're worried about your EAD at 6 msw . OK I am running numbers through almity's and nigel's formulae and coming up with the same result. What am I missing? __________________ Cheers, Dave.... Man is the only animal burdened with the knowledge he will eventually die
(Offline)

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