When I advanced to jet transport flying (altho 4-engine pistons were more fun, IMO), I was trained at PanAmerican on the Boeing 707.
Some of the old straight pipe models (early -320's for example) were very slow climbers at MTOW with an engine inoperative (V2 at 300 feet/min was not uncommon) so the 'positive climb' call was rather important.
These aircraft were equipped with KIFIS, so the v/s was not all that reliable.
PanAmerican insisted that the pressure altimeter be used, and if available, any other secondary indication...radalt for example.
Seemed reasonable to me.