You mean like net HP vs Gross HP? Pre 1972 auto manufacturers used Gross HP ratings then insurance companies started hemming and hawing at 400 HP motors and jacking rates through the roof, so they started rating them net, with all accessories functioning in '72. That's why people think the smog stuff killed the HP because the numbers dropped so much. The reality is the power didn't get smogged away till a few years later when catalytic converters became required.