Somehow the clock is displaying 24 hour time format. I want to get back to 12 hour format. How?

Push the mode button twice to enter the "set time" mode. Once the digital display is blinking, keep pushing "mode" until the PM display section in the upper left corner comes on. Once that happens you are back to the 12 hour clock. To set the clock, use the 1-4 buttons to set the hours and minutes.

Hope this helps.

Here's how it works on my si 686.

Push the mode button twice to enter the "set time" mode. Once the current time is blinking, advance hours by pressing 2 until it passes 12 midnight, and the display will be in 24 hour mode. 3:00 PM will be displayed as 15:00. Keep pressing button 2, advancing the hour past 24:00 (like a 25th hour) returns the clock to 12 hour mode.At that point set the time using buttons 1 thru 4 (1 hr-, 2 hr+, 3 min-, 4 min+). If you advance the hour past 11am to 12 noon, the PM indicator appears in the upper left corner because 12 noon is 12 pm. Likewise, when you advance the hour past 11pm to 12 midnight, the PM indicator disappears because 12 midnight is 12am. There is no AM indicator that displays, only PM.

To toggle the display between date, alarm, or temperature press the Display button.

To turn on the back light press the Snooze button.

If none of this works use a paperclip to press the RESET pin underneath the battery compartment's cover and try again.