how to calculate where your first decompression stop is

[dmaziuk]

True, but it is 85% of the way from ambient to the M-value line. In other words, GF0 is ambient pressure (zero supersaturation).

Well... when drawn on the back of a napkin, yes. Kind of.

 

[dmaziuk]

I've nearly figured out how to calculate the compartment pressures, but when it comes to gradient factors, I die lmao. because say I do 75/95 (example numbers, I wouldn't dive those lol), do I put in 0.75 or 75? or neither? for tissue compartment pressure, I assume I put in the value I get from Schreiner's equation?

Gradient factor is a simple proportion: at first stop it's GF Low, at the last stop it's GF High, the rest of the time it's between those two:

GF_slope = (GFHigh - GFLow) / (LastStopDepth - FirstStopDepth)

GFCurrent = GF_slope * CurrentStopDepth + GFHigh

 

[dmaziuk]

PS

https://www.shearwater.com/wp-content/uploads/2012/08/Deep-Stops.pdf

from horse's mouth

 

[EFX]

Gradient factor is a simple proportion: at first stop it's GF Low, at the last stop it's GF High, the rest of the time it's between those two:

GF_slope = (GFHigh - GFLow) / (LastStopDepth - FirstStopDepth)

GFCurrent = GF_slope * CurrentStopDepth + GFHigh

Using my example from above of GF = 60/80 and the first stop at 40 ft I get a slope of:
slope = (80 - 60) / (0 - 40) = -0.5
GFcurrent = -0.5 * 40 + 80 = -20 + 80 = 60 ;first stop = 40 ft
GFcurrent = -0.5 * 30 + 80 = -15 + 80 = 65 ;next stop at 30 ft
GFcurrent = -0.5 * 20 + 80 = -10 + 80 = 70 ;next stop at 20 ft

or alternatively:

gf_delta = (gf_hi - gf_lo) / (first_stop_depth / stop_interval)
= (80 - 60) / (40 / 10)
= 20 / 4
= 5

To calculate the next deco stop's gf add gf_delta to the current gf.
gf = gf + gf_delta
= 60 + 5 = 65 ;at the 30 ft stop
= 65 + 5 = 70 ;at the 20 ft stop
= 70 + 5 = 75 ;at the 10 ft stop
= 75 + 5 = 80 ;at the surface

 

[dmaziuk]

@kaylee_ann and yes, you calculate them in %: 65, 70, ..., but put in the fraction: .65, .7, etc.

 

[BlueTrin]

@kaylee_ann the picture on this blog entry shows the gf hi and gf lo (you should check that it matches the formulas before to trust it)

Surface GF and Other Teric Musings - Shearwater Research

Powerful yet Small Imagine having a tool that would give you a numerical percentage value of the decompression stress you would encounter if you were to instantaneously ascend to the surface. Not all dives are […]

www.shearwater.com

 

[kaylee_ann]

@kaylee_ann the picture on this blog entry shows the gf hi and gf lo (you should check that it matches the formulas before to trust it)

Surface GF and Other Teric Musings - Shearwater Research

Powerful yet Small Imagine having a tool that would give you a numerical percentage value of the decompression stress you would encounter if you were to instantaneously ascend to the surface. Not all dives are […]

www.shearwater.com

I don't see a picture, just a general article about how the teric offers several choices for gradient factors to customize your dive conservancy
a picture that shows GFs anyway* maybe im just tired and missing it

 

[BlueTrin]

I don't see a picture, just a general article about how the teric offers several choices for gradient factors to customize your dive conservancy
a picture that shows GFs anyway* maybe im just tired and missing it

I see this in the middle of the article

 

[kaylee_ann]

I see this in the middle of the article

View attachment 795007

OH I was literally looking for a picture of the watch with the gradient factors the diver used on the screen.....
man I don't even know anything anymore lmao, if I ever did it's gone now LOL

 

[LFMarm]

Using my example from above of GF = 60/80 and the first stop at 40 ft I get a slope of:
slope = (80 - 60) / (0 - 40) = -0.5
GFcurrent = -0.5 * 40 + 80 = -20 + 80 = 60 ;first stop = 40 ft
GFcurrent = -0.5 * 30 + 80 = -15 + 80 = 65 ;next stop at 30 ft
GFcurrent = -0.5 * 20 + 80 = -10 + 80 = 70 ;next stop at 20 ft

or alternatively:

gf_delta = (gf_hi - gf_lo) / (first_stop_depth / stop_interval)
= (80 - 60) / (40 / 10)
= 20 / 4
= 5

To calculate the next deco stop's gf add gf_delta to the current gf.
gf = gf + gf_delta
= 60 + 5 = 65 ;at the 30 ft stop
= 65 + 5 = 70 ;at the 20 ft stop
= 70 + 5 = 75 ;at the 10 ft stop
= 75 + 5 = 80 ;at the surface

Can all these calculations be done with your Excel model of decompression?HOME | My Site