ceiling/GF

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lermontov

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i read somewhere you can miss the stop depth as outlined on your DC and go to the ceiling depth but what does the ceiling represent -is it the M value of your dive profile or the ceiling of the GF you have chosen.

or is it simply the ceiling representation if your deco steps were smaller .

eg you have 3m steps outlined on the DC but when you get to say 9m your only staying there because the DC tells you to but real GF ceiling is actually 7.5 m but you cant go there because its not a multiple of 3m
 

Shearwater

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Hi, @lermontov . The ceiling is not an M-value unless you are using 99/99 as your gradient factors. Your second scenario is correct. Perhaps the graph below clarifies things. The ceiling would be the dotted orange line.
upload_2018-9-27_10-37-16.jpg

We do not recommend breaking stop depths, even if in doing so you stay under the ceiling. There is little or no data comparing the risk differences between doing stops in 3 m intervals vs following a continuous ceiling as your ascent. Some people have talked about following the ceiling as a way to speed up your ascent during an emergency situation. The point being that it is not a standard practice and we do not know what risks this practice might bring.
 

lermontov

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thanks for that all makes sense

ps on a technical note you GF Lo scale should be reading vertically as the G/F is a ratio between AP and the M value at a given depth, the scale as youve drawn it is a ratio over a reducing depth :)
 

rsingler

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on a technical note you GF Lo scale should be reading vertically
Well, actually, it doesn't matter, if drawn properly. What Shearwater's horizontal scale represents is the intercept of a line drawn to an unseen vertical scale, with the top edge of the graph. It just happens to be horizontal because that fits better. A vertical scale would just waste unused space at the top of the chart.
 

lermontov

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Well, actually, it doesn't matter, if drawn properly. What Shearwater's horizontal scale represents is the intercept of a line drawn to an unseen vertical scale, with the top edge of the graph. It just happens to be horizontal because that fits better. A vertical scale would just waste unused space at the top of the chart.
agreed it doesnt matter if the G/F was say 50/50 as the scale would be correct but a I said its a technical point - its more efficient as an illustration drawn like that
 

leadduck

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Well, actually, it doesn't matter, if drawn properly. What Shearwater's horizontal scale represents is the intercept of a line drawn to an unseen vertical scale, with the top edge of the graph. It just happens to be horizontal because that fits better. A vertical scale would just waste unused space at the top of the chart.

I beg to differ but it does make a difference, because the M-value line is not parallel to the ambient pressure line (b<1), particularly for the fast compartments that determine the first stop. In the plot above, the dotted orange line is probably close to a GF20/80 line, not GF30/80.
 

lermontov

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not just a great product but integrity and humility!
 

KenGordon

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Point well taken. Thank you for bringing this to our attention. We corrected the chart.
GF-graph.svg
Since this has turned into Pedants Corner, now you have GF as 30 at some depth below the start of the ascent.
 

lermontov

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Since this has turned into Pedants Corner, now you have GF as 30 at some depth below the start of the ascent.
lol yes your right
 
https://www.shearwater.com/products/peregrine/

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