I would not get too balled up about GTR function. I just don't think it offers much utility.
If you think about it, technical/advanced divers don't need GTR calculations on their computer to figure it out, and should have planned all that in advance. They understand their consumption rate and effect of depth (and hopefully have enough gas that what is really limiting the dive is the dive plan/deco anyway) and turn the dive when they hit their planned turn pressure.
Less experienced divers, on the other hand, who might "benefit" from a GTR calculation because they don't do that kind of planning might be inclined to put too much faith in it. It's usually just a snapshot based on the last 90 seconds or something of tank pressure change. It would be worse than useless if you had an issue, went deeper, etc.. Your 20 minutes of GTR will turn into 3 minutes in a panic. I think it can breed a false sense of security. GTR is not a guarantee and I'm not sure some divers understand that.
If you think about it, technical/advanced divers don't need GTR calculations on their computer to figure it out, and should have planned all that in advance. They understand their consumption rate and effect of depth (and hopefully have enough gas that what is really limiting the dive is the dive plan/deco anyway) and turn the dive when they hit their planned turn pressure.
Less experienced divers, on the other hand, who might "benefit" from a GTR calculation because they don't do that kind of planning might be inclined to put too much faith in it. It's usually just a snapshot based on the last 90 seconds or something of tank pressure change. It would be worse than useless if you had an issue, went deeper, etc.. Your 20 minutes of GTR will turn into 3 minutes in a panic. I think it can breed a false sense of security. GTR is not a guarantee and I'm not sure some divers understand that.