Where are the instructions? – Smart Measure-Measuring Tool Review

I have a degree in physics and advanced mathematics, and I don’t know what I am supposed to do to use the app. It tells me my office wall is over 30 feet away, I see a frame around the person in the example, but all I ever see on my phone is a grid that shrinks in the distance like a Star Wars introduction. There is a slider on the left, I have no clue as to what that is supposed to do or what it is telling me. Could we please have some instructions? The sample video shows somebody aiming the camera at a tree, but no instructions on how to read what I am looking at.
Review by BobKistler on Smart Measure-Measuring Tool.