Respectfully suggest to you that you do the following " exercise" three times: 
Weigh a cup of flour  and put is aside . Another cup weigh it and put aside , and another one , You will find out that my assertion in correct!
You might want to try this with any volume based  measure device,( spoon, tea spoon etc  etc . And of course the  scale has to me metric in single grams.
Especially for small batches accuracy is a must . Unfortunately  this  is not taught.