Blackberry 7510 User Manual page 106

Appointments in your handheld calendar that are
older than the number of days that you specify in
the Keep Appointments field are removed from
your handheld. The appointments can be restored,
however, if you set the Keep Appointments field
to a longer period of time. When you increase the
amount of time in this field, any appointments in
your calendar during that period of time appear in
your handheld calendar.
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