Well sir, it is apparent that you have not used one. They are a great tool for loading accurately, but being a machine, they need to be checked and confirmed regularly. There is usually a "check weight" included when you buy a scale. They are also susceptible to power surges and other disturbances. And no, it is not easy to know when they have been subject to a fluctuation event.
Also, I double check all aspects of loading in any run to prove consistency throughout. Using a gravity powered tool to cross check periodically, is just good practice.
The beauty of a scale like the A&D, is that you can load charges to .02gr consistently, at a rate of 6/minute (+/-)