Do not overlook the vital difference that striking away from the dead centre of the cue ball makes.
It is not merely a question of side or no side, top or no top, screw or no screw.
A cue ball that is struck only an eighth of an inch away from its centre behaves altogether differently from one struck true or even from one struck a quarter of an inch from its centre.
Professional players get to know all these small, but vital, differences and exploit them accordingly.
Thus, for a very slow, square screw they strike very low, whereas when the angle is only rather more than half-ball the minutest possible distance below the centre is sufficient.
The point that is sought to be impressed, and which is really a most important one, is that the scientific grading of compensation in cue contact is of extreme value in billiards position play and that in applying such compensation every eighth of an inch vitally counts.
In screwing do not vary the distance of cue contact below the centre.' The necessary differences in throw-off are better provided for by thicker or thinner ball contact and greater or lesser force.