Nautic S: locate live gradient factors (GF surface) in the 141-byte extended-status chunk

[latishab]

Summary

On the Nautic S (141-byte extended-status chunk, device "Ylivieska"), the parser emits no live gradient-factor samples, so there's no per-sample GF surface value. The full-size Nautic/Ocean (195-byte chunk, "Vaasa"/"Porvoo") does record it. Only the GF low/high setting decodes on the Nautic S, from /Summary.

What the captures show

Decoded straight from the corpus .bin files:

dive	device	chunk	GF samples	gfSurface
1787752091	Vaasa (Nautic)	195 B	244	up to 109
1788090406	Vaasa (Nautic)	195 B	390	up to 25
1787040311	Ylivieska (Nautic S)	141 B	0	—
1787214202	Ylivieska (Nautic S)	141 B	0	—
1787991757	Ylivieska (Nautic S)	141 B	0	—
1788596617	Ylivieska (Nautic S)	141 B	0	—

Why

In suunto_nautic_parser.c the GF record (vendor kind 5) is emitted only when chunk.size >= 192:

// gf99 @186 and surface @190 sit past the cylinder array; the
// leading-tissue GF @78 is inside that span ...
if (callback && chunk.size >= 192) {
    int gf99    = (int16_t) array_uint16_le (chunk.data + 186);
    int gf_surf = (int16_t) array_uint16_le (chunk.data + 190);
    int gf_lead = (int16_t) array_uint16_le (chunk.data + 78);
    ...
}

gf99 (@186) and gf_surface (@190) are past the end of the 141-byte Nautic S chunk, so the emission is gated off for that firmware. Offset 78 (leading-tissue GF on the 195 B layout) even falls inside tank slot 2 on the short chunk, so it can't just be shifted down.

Open question

Two possibilities, not yet distinguished:

1. The Nautic S (budget model) simply doesn't log real-time tissue/GF telemetry, and the 141-byte chunk carries no GF fields at all.
2. It logs GF at some unmapped lower offset in the 141-byte chunk that we haven't reverse-engineered.

The blocker to resolving it: no ground truth. The Suunto app's JSON export contains no gradient-factor field anywhere (only atmospheric SurfacePressure), so even for the 195-byte watches gfSurface is validated only by plausibility, not against an app value.

What would help

A Nautic S dive where the surfacing GF can be read off the watch screen (or app UI) at a known moment, so we can hunt for that value at a specific point in the 141-byte chunk. A raw .bin for such a dive would let us test candidate offsets.

@urbamax if any of your Nautic S dives show a GF/surface-GF number you can note, that would give us the anchor we need.

[latishab]

@urbamax doesn't have any Nautic S dives, so no anchor from there. Tracking this under the #29 umbrella instead: it needs a Nautic S (device "Ylivieska") dive from any owner where a surfacing-GF number can be read off the watch, so we can map it in the 141-byte chunk. No rush, parking it here until such a capture turns up.

[latishab]

@nandodiver @K4pisa @kreitje you're our Nautic S owners, so tagging you for a quick check.

On the Nautic S we currently get no live gradient-factor value out of a dive, only the GF low/high setting (e.g. 40/85). Before we go digging in the raw data, we'd like to know whether the Nautic S even shows a gradient factor to you at all:

• On the watch itself, during or right after a dive, does it ever display a GF / "GF99" / surface-GF percentage?
• In the Suunto app dive log for one of your dives, is there a gradient-factor number shown anywhere (surface GF, GF99, tissue loading, etc.)?

If yes, just note the number and which dive (date/time) it's from. That gives us a value to match against and confirms the watch actually records it. If neither the watch nor the app ever shows a GF number, that's a useful answer too, it likely means the Nautic S just doesn't log it. Thanks!