POLAR S720i - Manual (Page 99)

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cause erratic readings. Check your surroundings and move further away
from the source of disturbance.
...the display is blank or fading?
If the display is blank, activate the wrist receiver by pressing the OK button
twice, after which the Time of day display appears. The first sign of a
discharged battery is the battery symbol on the display. Also the digits fade
when the backlight is used. Have the batteries checked.
...there are no reactions to any buttons?
Reset the Polar heart rate monitor. Resetting clears watch settings which
will return to the default settings. User information and measuring
units settings will be saved.
1. Press the RESET button with a pen tip. Display becomes full of digits.
If you don’t press any button after reset within one minute the wrist
receiver returns to the Time of day display.
2. Press any of the buttons once. Time of day is displayed.
...the battery of the wrist receiver must be replaced?
We recommend having all service done by an authorised Polar Service
Centre. The guarantee does not cover damage or consequential damage
caused by service not authorised by Polar Electro. Polar Service will test
your wrist receiver for water resistance after battery replacement and make
a full periodic check of the complete Polar Heart rate monitor.
...there are irregular speed, distance or heart rate readings?
You may have come within range of strong electromagnetic-signals, which
cause erratic readings. Check your surroundings and move away from the
source of disturbance.