Tech- How are sleep study scored?

Some years ago on another forum, there was a tech forum for sleep techs that discussed scoring or interpreting sleep data for the report to the doc.
It seemed several hours were required to properly interpret one. There was a very wide variation in the times of different labs and made me question the accuracy of the reports.

Anyone know the present standards for such scoring?
How much is done by computer and what is involved?
Is this more or less accurate than auto generated data?

This seems to be a very ignored topic.
Tom