Because the project is powerd by a 9V battery, every mA of current plays a role. By default the display background illumination is quite bright. that cost about an extra of 15 mA of current. By replacing the jumper of the display illumination by a resistor (in my case 1KOhms) the current dropped a lot. So the display was still bright enough to read the text. Also I removed the Power LED on the Arduino Pro mini. This saved me another 5 mA. Finally the Scale takes in operation about 55mA of current from the 9V battery.