add framed binary telemetry transport

docs/calibration-2026-08-17.md

@@ -31,6 +31,11 @@ coefficients:
 | Y | -4.400892 | 259.825135 | 3.848742 |
 | Z | +11.776132 | 245.755573 | 4.069084 |
 
+The retained digits make the firmware calculation reproducible; they are not a
+claim of sub-count measurement accuracy. Independent face selection changed the
+derived values by up to about 0.03 counts, and repositioning changed a face mean
+by about one count.
+
 Firmware converts a mapped raw value to integer milligravity with:
 
 ```text
@@ -52,14 +57,25 @@ The central five thousand samples of the flat stationary interval produced:
 | Z | -7.0238 | 10.4259 |
 
 The instructed positive motion was top/USB-edge lift for +X, left-edge lift for
-+Y, and counterclockwise rotation viewed from the cover for +Z. Every outward
-stroke was positive on its intended gyro channel, and every return stroke was
-negative. Axis assignment and polarity are therefore confirmed.
++Y, and counterclockwise rotation viewed from the cover for +Z. Accelerometer
+tilt kinematics independently confirmed X and Y polarity. Rotation around Z while
+flat is rotation around gravity, so the accelerometer cannot independently check
+that sign. Z polarity follows from the right-handed enclosure frame, the
+right-handed L3G4200D frame, the identity gyro mapping, and the verified X/Y
+polarities. Axis assignment and polarity are therefore confirmed.
 
 Firmware subtracts the measured zero-rate bias and converts with the nominal
 L3G4200D +/-500 dps scale of 17.5 mdps/LSB. Gyro scale itself was not measured
 because no controlled angular-rate reference was available.
 
+The compile-time bias is only an initial correction. Twelve quiet stretches in
+this session showed real zero-rate wander of roughly 50 mdps on X/Z and 72 mdps
+on Y; the separate smoke capture differed by up to 63 mdps. That is enough to
+accumulate several degrees per minute if integrated. Runtime re-zeroing during a
+verified stationary interval is required before fusion, heading integration, or
+turn counting. Raw gyro counts therefore remain authoritative in the binary
+record.
+
 ## Freshness under motion
 
 Using gyro magnitude greater than 500 counts from stationary bias as a
@@ -86,4 +102,10 @@ and checked with a 3,814-record flat smoke capture:
 - Mean bias-corrected gyro: (+25.4, -62.9, -54.8) mdps
 
 The small residual horizontal acceleration is consistent with the enclosure not
-being perfectly level. The largest residual gyro mean is 0.063 dps.
+being perfectly level. The largest residual gyro mean is 0.063 dps, which is
+evidence of the fixed-bias limitation described above rather than a long-term
+heading guarantee.
+
+The two floating-point startup metadata lines were subsequently observed after a
+live device reset. They rendered the intended float32 calibration values before
+the binary stream began.