Rigol DS6104 - Page 270

RIGOL 13 System Function Setting
13-14 DS6000 User’s Guide
 Backspace: press this softkey to delete the characters in the "Option License
Input Area" from the right to the left.
 Clear: press this softkey to clear all the characters in the "Option License Input
Area".
 Apply: press this softkey and the oscilloscope will activate the corresponding
option using the option license currently input.