La Crosse Technology WS-9055TWC Instruction Manual page 11

When setting up multiple remote
temperature sensors, it is important to
remove the batteries from all existing
units in operation, then to insert batteries
first into all the remote temperature
sensors. Second install batteries into the
indoor weather station and do not press
any buttons for ten minutes.
Transmission problems will arise if this
is not done correctly.
To view the temperature of a different
remote temperature sensor unit, press
and release the "CH" button. A shift
from one number to the next should be
observed in the OUTDOOR LCD.
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