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Posted : March 10, 2009
hi, I read in another post about how you mark the line on your spool to help with deco stops. I am planning to do this but had a question before I get the permanent markers out.
Would you take into account how far under water the line starts? i.e do you put a 3 meter mark three meters down the line and do any 3m deco stops a little above that mark bearing in mind that you have at least a foot or more of DSMB under the water before the line starts, or do you estimate and put the 3m mark at about 2.5 meters down the line assuming the distance between the top of the line and the waters surface is about half a meter? What depth the line starts will vary depending on how full the DSMB is, or how much water got in.
Answer
Posted : March 10, 2009
Hi there,

Next time you dive in a lake tie off with a full DSMB what the 6m mark is then you can work out the rest !

That's what I did - taking of course the average from the computers and d-timers as to what the depth is. As I'm sure you know you don't have to be very precise for doing your deco at a given stop - but you do have to be consistent and not bounce around at your stop (mitigating cavitation and the effects of ppN2 or ppHe bouncing around between a higher and lower pressure - thereby causing a tension that can cause bubble formation and hence a bend).

So long as your markings are all about right +/- 8 inches or +/- 20 cm, then you will be fine. Mark the line as I suggest down to a sensible level for your qualifications and need.

Remember this is a safety measure to get you out of a complete instrument failure (incl backup). It does give you a nice reasurrance doing long deco stops to know the computers are telling the truth; Though I must admit a few times i've been glad the line is marked given the deco I've had to do...

Hope this helps, Andrew.
Answer provided by ADM Diving

Andrew Dawson-Maddocks
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