Garmin Personal Navigator GPS 100AVD Owner's Manual page 61

NOTE: Your altitude and climb rate should be controlled only by the pilot in
command with due regard for airspeed and other aircraft performance
limitations.
You will be informed with the message "START ALTITUDE CHNG" when
you are less than 15 seconds from the point at which the desired VNAV
maneuver is to begin. You will be informed with the message "FINAL
ALTITUDE ALERT" when the recommended altitude is within 1000 feet of
the final altitude. The VNAV function will be cancelled automatically if the
active route is changed in any way (e.g., using the GOTO function or adding
a waypoint.) You will be informed with the message "VNAV CANCELLED",
if this occurs.
See Section 12.4 for an application example using the VNAV function.
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