I have two different readings with 2 consequetive measurements. What is wrong?
You must have moved the scales right before one of these two measurements and the scales must have been switched on during this replacement. If you are moving the scales during calibration (=when the 0.0 reading changes from blinking to a fixed 0.0 reading) it will not give a reliable reading. You should redo the measurement, without moving the scales right before a measurement.