with UI datepicker i have two buttons to select previous and next month problem

with UI datepicker i have two buttons to select previous and next month problem

My goal is to have two buttons to select previous and next day. (I tried it with 'm' for months: same defect).

This is my code: 

$('#oneDayBack').click(function(){
                    $('#datePicker').datepicker('setDate', 'c-1d');
                    alert($('#datePicker').datepicker('getDate'));
                    });
                $('#oneDayFwd').click(function(){
                    $('#datePicker').datepicker('setDate', 'c+1d');
                    $('#datePicker').datepicker('refresh');
                    });

The alert is my debugger. It proves to me that the datePicker does understand that the selected date has been changed, since I get the newly selected value (one day before or after today). But I never get any farther than one day from some old conception of the current date. The refresh method doesn't help there.