We are a machine shop which services the aerospace industry. For visual inspections under microscope, we use 10x as our standard power whenever the customer has not specified a different one. Recently, one of our customers rejected one of our parts and, when we couldn't see any defects at 10x, were informed that they inspect at 30x. This customer had not specified any particular requirement on the print or PO. Question: is there any reference manual or standard that could help guide us on this subject? Thank you in advance.