I don't even know how I would do that.
1. Go to HD, Mart, etc and get a $5 kit for testing pH or pH and fertility. You take a small amount of soil, mix it with water to make a slurry and pour a little of the water into a reagent.
2. Get one of the meters from the same place. They may or may not be very accurate.
3. Take a soil sample to your local county extension agent. They do a test for about $10 that will tell you everything you need to know about your soil. They will explain how to do it there.
I am not familiar with a product called Cornerstone. Do you know if this is a fertilizer, weed killer or what? May just be one I haven't used.