NaN in DsAlt Copter 3.6.10

I have recently built a 50cm Quadcopter which seems to fly basically ok. The flight log however shows NaN in DsAlt. Is there any significance in this ?
Log File C:\Users\Douglas\AppData\Local\Temp\tmp138.tmp.log

Size (kb) 12526.9814453125

No of lines 148162

Duration 0:07:27

Vehicletype ArduCopter

Firmware Version V3.6.10

Firmware Hash 1c04a91e

Hardware Type

Free Mem 0

Skipped Lines 0

Test: Autotune = UNKNOWN - No ATUN log data

Test: Brownout = GOOD -

Test: Compass = GOOD - mag_field interference within limits (11.81%)

Max mag field length (950.60) > recommended (550.00)

Test: Dupe Log Data = GOOD -

Test: Empty = GOOD -

Test: Event/Failsafe = FAIL - ERR found: FS_BATT

Test: GPS = GOOD -

Test: IMU Mismatch = GOOD - (Mismatch: 0.24, WARN: 0.75, FAIL: 1.50)

Test: Motor Balance = GOOD - Motor channel averages = [1584, 1633, 1625, 1623]

Average motor output = 1616

Difference between min and max motor averages = 49

Test: NaNs = FAIL - Found NaN in CTUN.DSAlt

Test: OpticalFlow = FAIL - FAIL: no optical flow data

Test: Parameters = FAIL - ‘THR_MIN’ not found

Test: PM = GOOD -

Test: Pitch/Roll = GOOD -

Test: Thrust = GOOD -

Test: VCC = UNKNOWN - No CURR log data

We sometimes use “quiet NaNs” to indicate “no valid data”. They’re meant
to be used as flag values (in a desired-alt field you definitely don’t
want to say “0” if you’re actually not desiring an altitude!).

I believe that is one field where we do use them. Which mode were you in
at the time - would you expect there to be a desired alt? A
pilot-throttle mode like stabilize will obviously not have a desired


The “S” part of the DSAlt is for “Sonar” so if there’s no range finder present then it’s probably valid that it’s NaN.