N2 Loading VS SurfaceGF

I dive with a Shearwater Teric as my primary computer & Garmin Descent G1 as my backup. I use the SurfaceGF on my Teric to help me make a decision about whether I am safe to surface or off gas for a little longer etc. Both computers are set to identical custom gradient factors. End dive delay is also set to 2 minutes on both computers.

I understand that both computers use the same Buhlmann ZH-L16 Algorithm.

I also understand that Shearwater's SurfaceGF information is relative to M-value, and hence is not influenced by my gradient factor settings.

On my last dive, I noted an end SurfaceGF of 16% on my Shearwater, however on the Garmin N2 Loading it records 42%. Both computers set to air with no other gasses configured.

Obviously these numbers are very different. I looked around for information about exactly how N2 loading is calculated on the Garmin but couldn't see anything?

Can the Garmin reps on this forum shed any light on how N2 loading is calculated?

Ideally I'd like it to be the same as my shearwater, N2 loading relative to M-value. Especially considering I'm venturing into technical diving where this kind of information must be accurate.

0 4745724 4 months ago

I've been wondering the same. What I suspect is that the number given is a percentage of the user set high GF. Mine is set to 80 and I got an end N2/He load of 85 % so the computer should not have let me end the dive with that much nitrogen in the system, but the number actually means 68 % of the M-value. This is obviously very stupid, why make an extra calculation which the user then needs to reverse (using a calculator) to get the information they want to know?

I've just sent an email to Garmin about this, I'll let you know what they respond.

My theory might also be wrong since with this logic (and if I know how to math) your high GF would be ~40 which is extremely conservative... Even more so would be nice to know how the value is calculated, and why oh why isn't it just a straight percentage of the M-value.

One thing that might effect is the altimeter in Garmin computers which Shearwaters don't have. My old misbehaving Mk1 would always climb kilometers on its own so I was altitude diving in the ocean. Would be nice if it'd auto calibrate with GPS for any given body of water - sea level should at least be easy and I'm pretty sure Garmin knows the topography of the whole planet so it should also know the altitudes of all water surfaces quite accurately.

0 6783570 12 days ago in reply to 4745724

Hey bud, in answer to your question, yes my GFHI at the time would have been around 40 - I was having some issues after diving and was trying to understand if it was due to decompression stress etc. We never got an answer from Garmin as to what the numbers in the N2/He actually mean, but that seems to be a common issue throughout the forums - no reply from Garmin

0 Vasilis K. 11 days ago

This is SERIOUS! Such issues have been reported in the past. This is supposed to be pro level equipment, and we're talking about major security things.