If you have followed me for a few years you know that I hate tape measurers, just because I hate making mistakes. That is why I love jigs.
When you want to drill all those evenly spaced holes in the cabinet sides, and all four support pins have to line up with each other or else the shelf will wobble, you are headed for trouble if you try to measure it all out -- especially if you are working under the counter half on your back.
The professionals have a special jig just for doing this that you can see in the first photo. Not only do you set up the whole rack of holes, but you have a drill guide that in conjunction with a drill stop, will make a perfectly straight hole just the right depth and in the right place.
For us common mortals you can get similar results by taking a piece of peg-board. Screw a guide on one edge so you can butt it up to the side of the panel you want to drill into, and slide it down to the bottom. With a felt pen, mark out which two rows you want to drill, and simply use the holes that are already there in a perfectly square grid to guide your drill. Use a stop on the drill to not go through the other side. For really professional results use a brad point drill which scores the circle before cutting out the wood, giving a perfectly clean entry for the pin.