Unfortunately restrictions

I recently, in Condor for 2 suitcases, each 1kg overweight EUR 20 - had to shell out, 'and that was not the first time in a charter pilot,' was now the purchase of a luggage scale on the program. The Soehnle 66172 was my favorite because of the many positive reviews and precipitated out of the box also for the following benefits:
- Great design, small + light (fits in your pocket)
- Wide grip, thus lifting the suitcase with 2 hands possible
- Easy to use, easy reading of the weight on the display. Display of the weight for about 5 min after discontinuation of the case.
The decisive factor is, of course, the measurement accuracy, especially in the area of ​​20kg, which is applicable to the majority of tourist flights per suitcase. The indication '100-g-exact division' on the packaging of the scale says yes only about the readability of the display, do not have a measurement tolerance guaranteed by the manufacturer, which can only be expected for certified scales. For my protection I have made the following experiment: For a reference weight I first an empty suitcase weighed (luggage scale 5.0kg; Bathroom Scale 5,2kg, 5,1kg average). In the suitcase were 15 water bottles each 1,07kg what a computational suitcases weighing about 21,2kg means and should be an about exact value. This value 21,2kg was confirmed by the weighing of the suitcase on the bathroom scales with 21,4kg. Now the luggage scale was off with 2 series of measurements at different times. The full case ever weighed 5x:

A. 20.2; 20.5; 20.8; 20.8; 20,6kg
B. 20.8; 20.7; 20.9; 20.8; 20,5kg

Conclusion: My luggage scale weighs to this investigation - 20,8kg set as common value - 400g less than the reference value. In future I will therefore before the return flight in the hotel every car 5x weigh and pack the suitcase on the luggage scale with 19,5kg average weighed weight, so even 0,5kg '' air '' to let the permissible 20kg for the suitcase. At home, I'm going to trust in my bathroom scale, which is not such a large spectrum of values ​​has as luggage scale, see measurements above.
Instead of the usual 5 stars I can only awarded 3 stars here.