User routine accuracy checks for Checkweighers

Regarding checkweighers used in pharmaceutical industry in filling applications:

Is it recommended to perform routine accuracy checks by production operator (similar to routine sensitivity tests performed by user on static scales) or it is sufficient to do only the challenge test for rejection mechanism performed periodically by production operator ??

and if it is recommended to perform routine accuracy checks by production operator:
1- this check will be performed using test weights (e.g OIML certified weights) , or will be performed using a representative package of the production line (after determining its actual weight using an accurate static scale) ?
2- and if performed using a representative package, the purpose will be checking Mean error or Standard deviation or both ?

???

Thanks a lot