Nice lil scale to have.  You have to turn the black dial to the top number, to calibrate it.  The dial stays at the weight recorded, so you can read it, after weighing your item.  I tried it out on my luggage, and received 2 differnt readings.  I then took my luggage to my regular scale, and the Smartrip scale was only 3-5 pounds, off.  I would say, it's still a good buy.  It's better to know "about" where you stand, before getting to the airline counter and being told you have to pay more, or get out of line, and choose which items are staying in luggage, and which shirts you have to start layering on.