John,
the zero column is the theoretical timing or "advertised" timing as it is now known, this is the actual timing at the point of lift and does not take into account the valve lash unless it is a hydraulic cam.
It is also virtually impossible to measure accurately as the lifter is moving so slowly in relation to crank degrees, hence the figures for .100 " lifter rise which is very easy to measure.
The norm nowadays is .050 lifter rise which is just as easy to check. In practical terms the first .050" of lifter movement has virtually no effect on performance but the movement there does effect how easy or otherwise the cam is on the rest of the valve train.
In all honesty why would you want a 1970 cam profile anyway, there have been huge advances in cam profile technology, why not take advantage. Similarly valve spring materials have improved, you needed a slow lifting cam like that one fourty years ago or you start busting springs. Look at the seat pressure specified, 85lbs, thats OEM street stuff now.
Mike
