Honeywell TB8220U Owner's Manual page 24

Setting Calendar
This thermostat is designed to, under normal use, automatically keep current time and day
in memory for up to ten years once the calendar is set. There are two ways to set the
calendar for this thermostat:
SETTING CALENDAR AFTER THERMOSTAT IS ALREADY FUNCTIONING
See steps 1 through 4, in the Advanced Settings section, to set year, month and day.
SETTING CALENDAR WHEN THERMOSTAT IS FIRST POWERED
When first powered, the thermostat proceeds through a sequence of screens to set the
calendar.
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