Education/document evaluating agencies have guidelines and usually USCIS/DOL agree with their evaluation.
Back in 1996, I had my engineering degree evaluated to get admission in Masters. They did an excellent job of not only evaluating overall equivalency but also they went into details. They took each course I did in undergrad and assigned credit hours and then graded them individually. They also gave overall GPA based on marks I received back in India and assigned total credit hours to the degree.
I have been using that evaluation for last 8 years for all immigration (F1, H1 and GC) as well as educational purpose and never had any problem.