The first two parameters let you specify range of the control. Try imagining a volume control on a stereo. It may have a lowest setting of 0 and a highest of 10. The first parameter lets you specify the lowest setting that the control can have. In our example, this is 0. The second parameter lets you specify the highest setting that the control can have. In our example, this is 10. Normally, you will assign these parameters with numbers in the XCMD line itself.
The third parameter lets you specify the inital setting of the control. In our example, the stereo might have been set to 2. The past tense is crucial here because if the user readjusts the control to 5, the next time ScrollControl is called it should set the initial setting of the control to 5 not to 2. Thus, you might want to assign these parameters using a variable that is used to collect the result.