M-values and Gradient Factors

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Remy B.

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Location
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I'm doing my Trimix course online before I go to the class room and I'm very puzzled in what it has been recommended by studies and experts regarding the setting of the GF.

So far I understood you want to stay away from your M-value because it is your supersaturation limit or where bubbles can form or the silent bubbles can multiply.

and lower cifers in the GF means the % of how close you are to the M-value, for example GF 30/70 means that some tissues are 30% out of 100% = far away ( 100% = M-value limit ) and 70% out 100% = near the M-value

Now it is said that you need to keep your self as far away from your M-value, but it seems that the trend it to get closer to that M-value by doing GF of 50/80 or 50/85, and to discern from the 30/70.

What did I miss or where I'm getting confused at ?
 
Not trying to be unhelpful at all, but this is probably a question that's best asked of your course instructor. Different people, (of which there are many on this forum), will each answer this question differently.
 
I can understand the Lower GF to be raised to a higher in order to get away from the deeper stops but to raise the Higher GF doesn't make much sense, only if you rally running out of gas
 
Now it is said that you need to keep your self as far away from your M-value, but it seems that the trend it to get closer to that M-value by doing GF of 50/80 or 50/85, and to discern from the 30/70.
As for the lower GF, staying as far away from it as possible is too simplistic a viewpoint. Carry that to an extreme, and you can never ascend. Stay down too deep for too long, and you will be ongassing too much in the slower tissues while you are supposedly trying to protect the faster tissues, which apparently are not in as much of a need for protection as some people formerly thought. Somewhere for a particular diver there is a perfect GF low for you, but research has not given us convincing evidence of where that is yet. Recent evidence is suggesting that 30 is too low, and most people I know have moved it up.

As for the GF high, you have to trade off your need for safety with the need to get out of the water eventually. Sure, keeping it at 70 is safer than 80, but if you think 80 is plenty safe but keep it at 70 for safety, you might be wondering about how safe you want things during that last extended stop when you are getting cold and really, really sick of staring at your buddy. What some people I know are doing is going with 80 or 85, feeling pretty sure they are safe when they get there, but then hanging around a while for that additional (theoretically unnecessary) extra measure of safety.
 
Watch this
Try planning a 30/70 version of your dive and compare it with a 50/80, 50/85, 70/70 or 80/80 one.

I stopped using 30/70 CCR when my OC buddy using a Zoop and diving 32% waved as she went to get tea and cake while I waited on the line at 6m with all the other GF mugs.
 
I'm doing my Trimix course online before I go to the class room and I'm very puzzled in what it has been recommended by studies and experts regarding the setting of the GF.

So far I understood you want to stay away from your M-value because it is your supersaturation limit or where bubbles can form or the silent bubbles can multiply.

and lower cifers in the GF means the % of how close you are to the M-value, for example GF 30/70 means that some tissues are 30% out of 100% = far away ( 100% = M-value limit ) and 70% out 100% = near the M-value

Now it is said that you need to keep your self as far away from your M-value, but it seems that the trend it to get closer to that M-value by doing GF of 50/80 or 50/85, and to discern from the 30/70.

What did I miss or where I'm getting confused at ?

I think you might have missed two things.

The first is that each compartment has its own instantaneous M-value; the one with the highest percentage of the M value at any given moment is called the "leading" or "controlling:" compartment.. The second is that the M-value allowed by your computer or planner increases from the first value (GF low) to the second (GF high) as you decompress. At a quick glance, this looks like a good article: Gradient Factors | Dive Rite
 
I'm doing my Trimix course online before I go to the class room and I'm very puzzled in what it has been recommended by studies and experts regarding the setting of the GF.

So far I understood you want to stay away from your M-value because it is your supersaturation limit or where bubbles can form or the silent bubbles can multiply.

and lower cifers in the GF means the % of how close you are to the M-value, for example GF 30/70 means that some tissues are 30% out of 100% = far away ( 100% = M-value limit ) and 70% out 100% = near the M-value

Now it is said that you need to keep your self as far away from your M-value, but it seems that the trend it to get closer to that M-value by doing GF of 50/80 or 50/85, and to discern from the 30/70.

What did I miss or where I'm getting confused at ?

Figure 4 in @TrimixToo 's link is a good graphic depiction of what you're looking for. One way of thinking about it is that the low gradient factor governs the depth of your first stop, and the high gradient factor governs the length of your last stop.

Best regards,
DDM
 
https://www.shearwater.com/products/swift/

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