During the build of the project i noticed that the scale values were drifting quite a lot. After a deep investigation into the problem it showed that the resistance of some of the used SMD parts on the controller are very sensitive. Even by breathing over the electronicss slightly the values drifted dramatically. So I decided to cover the electronics with some transparent varnish. The varnish after it was dry caused the drift of the controller to drop to almost zero. So my recommendation is to put some varnish onto the complete board after soldering everything together.