Premise: How to install a drawer slide in a lipped cabinet<br>First of all, you need to empty out the cabinet (the top shelf) and measure it. Now measure the cabinet lip from hinge. Make sure that you measure: the cabinet from the widest part of the hinge, inside of the cabinet, all corners of the cabinet, cabinet height from lip, if you need to install double stacked drawer system.
Hypothesis: The top shelf of a cabinet doesn't need to be measured when you are installing a drawer slide.