I have the georg jenson wave clock but don't know how to toggle between the 24/12 hour clock. Right now it's set for the 24 hour clock and I live in the U.S. and want the 12 hour clock setting.

To Set the DST and TIME ZONE
Press and hold the SET/WAVE button for couple of seconds and Calendar Mode will begin
To Set the Calendar

1. Press + or - button on the front sequentially to set year.
2. Holding down either + or - button on the front change the year at high speed.
3. Press SET/WAVE button to confirm year set and goes to date set.
4. Press + or - button on the front sequentially to set date.
5. Press SET/WAVE button to set the order of the month and year.
6. Holding down either + or - button on the front will change the order of the Month and Year.
7. Press SET/WAVE button to set the Time
8. Holding down either + or - button on the front change the time at high speed (AM or PM will be displayed).
9. Press SET/WAVE button to enter DST MODE

The DOWN button toggles between DST ON and OFF
The UP button toggles the time zones as Eastern, Central, Mountain, Pacific, AK-Alaska, HI Hawaii until your desired time zone shown on display.

1. Press SET/WAVE button to enter LANGUAGE MODE

Holding down either + or - button change the language to EN (English or your common language).

1. Press SET/WAVE button to enter Standard (12 Hour) or Military Time (24Hour) MODE
2. Press SET/WAVE button again to END and return to normal screen

Check setting switch, sounds like it's running on DST, Daylight saving time.

Press and hold SEL (select) for more than 2 seconds so that one of the PSM items appears on the display.
Press number 2 button to to select Clock (clock should be above the #2.
The Clock HR (Hour) setting will appear.
Adjust the hour using the round left side control.
Use the up/down arrows (right side) to toggle to Minutes and use the dial to set minutes.
Use the up/down arrows to toggle to 24/12 and choose between military time or standard
with the left dial.
Press SEL to save changes.
Here is what appears to be your manual. See page 9 for clock. Save the manual to
your computer for future reference if it is correct.

JVC KD-LH300 Manual

Instructions to set the C17D2090 atomic clock

A. To manually set the clock

1. Use the CAL/ALM button to toggle the display until it shows the calendar
2. Press and hold SET until the screen flashes "12hr"
3. Use the UP (antenna) and DOWN (alarm) buttons to change the settings
4. Press SET to set the value

This mode will let you set the 12/24 hours clock, the time, date and year. You should be in the right time zone before you start.

B. To set the alarm1 time

1. Use the CAL/ALM button to toggle the display until it shows the AL1 alarm time
2. Press and hold SET until the alarm time flashes
3. Use the UP (antenna) and DOWN (alarm) buttons to change the settings
4. Press SET to set the value

C. To set the alarm2 time

1. Use the CAL/ALM button to toggle the display until it shows the AL2 alarm time
2. Press and hold SET until the alarm time flashes
3. Use the UP (antenna) and DOWN (alarm) buttons to change the settings
4. Press SET to set the value

D. To turn on alarm1

1. Use the CAL/ALM button to toggle the display until it shows the AL1 alarm time
2. Use the DOWN (alarm) button to toggle the alarm on and off (a bell appears on the screen)

E. To turn on alarm2

1. Use the CAL/ALM button to toggle the display until it shows the AL2 alarm time
2. Use the DOWN (alarm) button to toggle the alarm on and off (a bell appears on the screen)

F. To have the atomic clock set automatically

1. Press and hold the UP (antenna) button until a little triangle flashes on the screen
2. Wait for clock to set
3. To give up waiting, press the UP (antenna) button again.

G. To change the time zone
1. Tap the ZONE button to toggle between the 4 time zones

I couldn't find the manufacturers' web site but I found the following , which may help;-

The unit automatically receives the time signal everyday at midnight and makes any required adjustment to the time displayed.

The WAVE OK indicator and the Tower Icon on the display will show if the time signal is successfully received or after manually pressing the SET/WAVE button

You can trigger a Signal Receive operation at any time by pressing the SET/WAVE button, which will activate the Signal Search function of the unit.
To Manually Set the Clock
To Set the Year and Date
1. Press SET/WAVE button after setting TIME ZONE and DST
2. Press + or - button sequentially to set the year (holding down the button will change the year at a high speed)
3. Press SET/WAVE button to confirm the year set and start the date process
4. Press + or - button sequentially to set the current date (holding down the button will change the date at a high speed)
NOTE: The weekday changes automatically depending on the year and date

To Set the Time
1. Press the SET/WAVE button after setting the calendar
2. Press + or - button sequentially to set the minutes (holding down the button will change the year at a high speed)
NOTE: Once you the press + or - button, the seconds will reset to 00

To set the 12/24 HR mode and the Temperature Mode
1. Press SET/WAVE button after setting the time
2. Press the + button to toggle between between 12HR and 24HR (military) modes
3. Press the - button to toggle between C and F temperature display mode
4. Press SET/WAVE button to confirm and quit the set mode

On first generation Bose, press "Alarm Setup" and "on/off" button to toggle between military and 12 our time.
Older model documentation:
http://www.bose.com/pdf/customer_service/owners/og_wrcd.pdf

The "mode" button is there to change the function of the + & - buttons.

If you press the mode button several times you will cycle through the various setting features of the clock.

Look for the one that sets the time zone and use the + or - buttons to select your zone.

Some experimentation may be required!

Setting the Clock
1) Press and hold in the BAND button [4] then press the DISP button [9] to toggle the display to the clock mode.

2) Press and hold in the BAND button [4] then press and hold in the DISP button [9] for at least 2 seconds.

3) Select left or right to adjust the time using the a-selector

~Adjusting minutes
Each time you select right >> using the a-selector [3], the minutes increment up by one digit (0 to 59).

~Adjusting hours
Each time you select left << using the a-selector [3], the hours increment up by one digit (1 to 12).
*The clock only displays time in a 12-hour format.
There is no way to toggle the clock to a 24-hour format.

4) Press the BAND button [4] to set the clock into memory. This also resets the seconds counter to zero.

Note:
*The clock can only be set by turning power on to the unit and switching to the clock display mode. You cannot set the clock when it is displayed with only the igntion on. If you drain or remove the car's battery, the clock must be reset. While setting the clock, if another button or operation is selected, the clock set mode is canceled.

With clock display on, hold left toggle until hours flash, set with right toggle then press left toggle once to flash minutes, set with right toggle.

On first generation Bose, press "Alarm Setup" and "on/off" button to toggle between military and 12 our time.
Older model documentation:
http://www.bose.com/pdf/customer_service/owners/og_wrcd.pdf