A drowsy worker may affect rubber quality badly.

THE WHOLE TRUTH OF MAKING TENERGY (or the suchlike).

New King James Version wrote: For nothing is secret that will not be revealed, nor anything hidden that will not be known and come to light.

This is the very reason for the racket coverings would play in different way from one batch to another batch. What if the worker came in a morning shift 8 a.m. drowsy or drunk?? This is why I always purchase rubbers from a factory in a large wholesale order. I've now got twice alert about the Japanese ''famous'' products since I'd got aware very well of the actual factory processes.
https://www.youtube.com/watch?v=

Be happy.