DEV-958: correct the rationale - 0.061 mg/LSB is real, not a rounding

My previous comment claimed ST's accel figures were just 32768/FS rounded to
three significant figures, and that the old derived values were therefore the
more accurate of the two. That was wrong, and the datasheet settles it.

AN5922 Table 27 (FS_XL = +-2 g) gives worked register contents: 1 g reads
0x4009 = 16393 LSB and 350 mg reads 0x1669 = 5737 LSB. 0.061 mg/LSB predicts
16393.4 and 5737.7; a 32768/FS derivation predicts 16384 and 5734.4. The
accelerometer does not map its nominal full scale onto exactly 2^15 counts -
it has a small margin, the same phenomenon as the gyro, just far smaller.

So the old values were wrong by 0.0576%, and this is a correctness fix rather
than a consistency trade-off. The constants themselves are unchanged from the
previous commit; only the reasoning recorded beside them.

Corroborated four ways: the datasheet worked example, ST's upstream driver
(STMicroelectronics/lsm6dsv-pid, byte-identical to the copy this firmware
vendors), every example in STMems_Standard_C_drivers/lsm6dsv_STdC/examples, and
lsm6dsv_self_test.c in particular - its pass/fail limits are specified in mg, so
ST's own self-test only produces correct results if 0.122 mg/LSB is right.

Comment-only; 51 driver tests still pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: marknolan

ShimmerDriver/src/main/java/com/shimmerresearch/verisense/sensors/SensorLSM6DSV.java

@@ -288,23 +288,27 @@ public static final class DatabaseConfigHandle {
 	// Accel sensitivity (LSB per m/s^2) from the ST datasheet linear-acceleration
 	// sensitivity: 0.061 / 0.122 / 0.244 / 0.488 mg/LSB, i.e. 1/(mg_per_LSB/1000)/9.80665.
 	//
-	// These were previously derived as 32768/(FS_g*9.80665), which is the exact form:
-	// unlike the gyro (see below) the accel really does span the full 16-bit range at
-	// its nominal full scale, so ST's printed figures are just 32768/FS rounded to
-	// three significant figures (2/32768 g = 0.06103516 mg/LSB -> "0.061"). The exact
-	// derivation is therefore 0.0576% larger and, on its own terms, slightly more
-	// accurate.
+	// These were previously derived as 32768/(FS_g*9.80665), on the assumption that
+	// the accel spans exactly the full 16-bit range at nominal full scale and that
+	// ST's printed figures were just that quantity rounded to three significant
+	// figures. They are not. The datasheet's own worked example (AN5922 Table 27,
+	// FS_XL = +-2 g) settles it: 1 g reads 0x4009 = 16393 LSB and 350 mg reads
+	// 0x1669 = 5737 LSB. 0.061 mg/LSB predicts 16393.4 and 5737.7; the 32768/FS
+	// derivation predicts 16384 and 5734.4. So the sensor really is 0.061 mg/LSB -
+	// full scale sits a little inside +-2 g - and the old derivation was wrong by
+	// 0.0576%, not merely a rounding apart from the datasheet.
 	//
-	// We use the datasheet figures anyway, for agreement rather than precision. The
-	// firmware seeds these exact values into the on-device calibration blob
-	// (SC_ACCEL_SENS in asm_calibration.c), so they are what the device itself
-	// reports and what becomes the source of truth once per-unit calibration is
-	// loaded; the web SDK catalog and the gen-1 SensorLSM6DS3/SensorLIS2DW12 classes
-	// use them too, as does ST's own reference driver (lsm6dsv_from_fs2_to_mg
-	// multiplies by 0.061f). Keeping the exact form here would leave a 0.0576% step
-	// change in calibrated output waiting to appear the day the device blob is
-	// honoured. 0.0576% is far inside per-unit sensitivity variation, so consistency
-	// is worth more than the last digit.
+	// Same story as the gyro below, just with a much smaller margin: neither part
+	// maps its nominal full scale onto exactly 2^15 counts, so for both of them the
+	// ST mg/LSB and mdps/LSB figures are the authority and a 32768/FS derivation is
+	// simply incorrect. These values also match the firmware calibration seed
+	// (SC_ACCEL_SENS in asm_calibration.c), the web SDK catalog, the gen-1
+	// SensorLSM6DS3/SensorLIS2DW12 classes and ST's own reference driver
+	// (lsm6dsv_from_fs2_to_mg multiplies by 0.061f). Every example in
+	// STMems_Standard_C_drivers/lsm6dsv_STdC/examples converts through those
+	// helpers and none derives 32768/FS - including lsm6dsv_self_test.c, whose
+	// pass/fail limits are specified in mg, so ST's own self-test only comes out
+	// right if 0.122 mg/LSB is the true sensitivity.
 	public static final double[][] SENS_ACCEL_2G  = {{1671.665922915,0,0},{0,1671.665922915,0},{0,0,1671.665922915}};
 	public static final double[][] SENS_ACCEL_4G  = {{835.832961457,0,0},{0,835.832961457,0},{0,0,835.832961457}};
 	public static final double[][] SENS_ACCEL_8G  = {{417.916480729,0,0},{0,417.916480729,0},{0,0,417.916480729}};