Begin by pressing and holding the SET button.  Next press and hold the PROG/MAN button.  Release both buttons.  The current time of day will appear on the display.  Set the clock to the correct time by pressing either the down or up buttons.  The time will adjust by minutes.  When the correct time is set press and release the SET button.  The day of the week will be displayed.  Press either the down or up buttons to display the correct day of the week.  1=Monday and so on to 7=Sunday.  Press and release the SET button.  The differential setting will be displayed.  Press either the down or up buttons to select the preferred setting of 1, 2, or 3 degrees. If you have a 9615 or 9620 press the set button to get to the second stage differential which is adjustable from 2-6 degrees.  Press and release the SET button or wait 45 seconds and the display will return to its normal mode.