adjustable control arms

hello, new to the forum and was wondering if I could get some advice. im about to install a 4.5" rc lift with the adjustable control arms...question is how do you adjust the arms to the length....do you measure the factory arms and adjust to that length or just take it to a mech to have adjusted.

Measure from the center of one bolt hole, to center of the other bolt hole. Adjust as needed.

This chart has been posted often:

Thanks that helped a lot.