Not sure if I'm doing something wrong, but even after reading the instructions & watching the video I'm getting odd results which don't match what is in the vid

Not sure if I'm doing something wrong, but even after reading the instructions & watching the video I'm getting odd results which don't match what is in the video at all. I realize there is a disclaimer that it may not necessarily be accurate, but it varies between 0 and some wildly innacurate value like 30 cm when I'm holding it 1 or 2cm away.