a graphical tuning system for computer - controlled radio equipment , where a two - dimensional tuning field is displayed with one axis representing frequency and the other axis representing tuning resolution . the user tunes the equipment by moving a pointer in this two - dimensional field . a spectrum display may be superimposed as a third dimension on a two - dimensional tuning field with one axis representing the frequency , the second axis representing tuning resolution and the third axis representing the signal level . the preferred tuning relationship is described by the generalized equation : f 2 = f 1 +* fr , where f1 is the old frequency , and f2 is the new frequency , where x1 , y1 are the new co - ordinates of the mouse , x2 , y2 are the old co - ordinates of the mouse , and fr is a function describing a relationship between the position of the mouse and the frequency resolution .