Oven qualification

Dear all,
Based on my project, I have to qualify oven performance. I’ve heard that for heat distribution study(load and unload) and heat penetration study, we should to know the difference temperature that shown in oven display and thermocople and also the difference temperature between its thermocouples. Any special term for this criteria?
Some said that FDA 2008 regulation told that the difference must be 15 C when it’s unload and 30 C when it’s load. Is it right? Because I could’nt find this term in FDA website. Any opinion or recommended article about this?

Your reply is really helpfull.

Best regards,