I was playing around with my new range finder and got some odd readings. I was ranging my back stop where I have got targets setup and got different readings . On the light silver color metal it read 34 yards with is what it actually is. On the brown rusted metal it read 35 yards, on the black rubber matting that is attached to the metal backing it read 37 yards. All three materials are 34 yards. Does color of object make a difference when measuring? Is this normal or is my range finder defective?