Later in the Tang dynasty , Cao Rou ( æ æ '' ) and others simplified the notation , using only the important elements of the characters ( like string number , plucking technique , hui number and which finger to stop the string ) and combined them into one character notation . Later in the Tang dynasty , Cao Rou and others simplified the notation , using only the important elements of the characters ( like string number , plucking technique , hui number and which finger to stop the string ) and combined them into one character notation .