Validation class and link with ISU data

hello,

I wanted to understand how validations linked with validation classes (maintained at rate level) gets triggered everytime we enter a meter read. As we know tolarence limits etc that determine max allowed MR in a period are determined by validation classes. But what I am trying to understand is - how does a VC linked at rate level tie with meter read entered at device/register level (because rate gets executed only during billing, so how does it ensure MR validations are run).. there must be a link somewhere that ties VC with register.

Example : a device with kwh and kva register, rates that calculate kva or kwh have seperate validation classes. How is MR entered in kwh register linked to validation class for kwh (and not for kva).

Thanks!

AM