RIGOL  Chapter 4 To Set the Sample System   
4-12  MSO7000/DS7000 User Guide 
After you select "User", press Expand User and then rotate the multifunction 
knob    to set the expansion reference. Its available range is from the 
rightmost position of the screen to the leftmost position of the screen. By default, 
it is the screen center. Pressing down the multifunction knob    can quickly 
reset the user-defined reference position to 0. 
 
Note: This function is unavailable in YT mode with the delayed sweep being enabled, 
XY mode, and ROLL mode.