9.0 D.S.T. is on
9.1 D.S.T. is off
From the manual:
The user may choose to operate with DST or without DST.
The default setting, at power-on, employs DST
To turn DST OFF, perform the following:
1. Turn detector off.
2. Press-and-hold the red MENU button and
push-forward-and-hold the TOGGLE SWITCH.
3. Turn the detector on, while you are still holding the controls.
4. Continue to hold the controls.
5. See the "90" displayed.
6. Rotate SETTINGS KNOB clockwise.
7. See "91" displayed.
8. Release the MENU button and TOGGLE SWITCH.
Upon release of the controls,the detector will operate WITHOUT DST
DST status is saved to memory after the user performs this procedure.
Each time the detector is powered back on, it will continue in the programmed setting.
The same procedure is used to turn DST back on, except that the SETTING KNOB is turned
counterclockwise to change "91" to "90".
DST can be turned on or off as desired, but each change requires the user to first power the
detector off.