Suunto D9tx User Manual page 35

NOTE
Strong electromagnetic fields, such as power lines, stereo speakers, and magnets
can affect the compass calibration. Therefore, it is advisable to calibrate the compass
if your Suunto D9tx has been exposed to these fields.
NOTE
NOTE
36
The unit will automatically enter the calibration sequence when
taken into use for the first time.
When traveling overseas, it is recommended that you recalib-
rate the compass at the new location before using it.
Remember to hold the Suunto D9tx level during the calibration
process.