It must not be imagined that hand play and strokes are merely of the freak variety and have no real billiard value.
The billiard ball, when twisted by the hand, and carefully observed, reveals some instructive lessons.
In the first place, it discloses the enormous potentialities of side in substitution for force, and, in the second place, it opens the mind of the average player to the very real differences that result in the run of a slow side-laden ball in different directions on the table.
Stand at the baulk end of the table and spin a ball so that it travels slowly up the board. It will inevitably veer gradually to the left. Now go to the spot end and repeat the process, and the veering will be found to be to the right. Next stand at the side of the table, sending the ball spinning gently across, and no deflection will be noticed, because the nap influence is now negligible.
The total deflection in a table length is fully one inch, but in contrary directions, and this deflection is gradual and progressive. Consequently a check side slow stroke must be aimed an inch line to ensure half-ball contact after running a table length: half an inch for half-table length; and a quarter of an inch for quarter-table length.
Down the table the aim would be fuller than half ball in the same proportions, whilst with slow running side the whole thing would be exactly reversed.
More frequently, however, the strokes are, by preference, played faster, in order to bring the object ball back up the table, and under these conditions the side ceases to operate, except at the pocket shoulder, when it is, furthermore, favouring, instead of opposing, side.
Still there are many strokes that call for slow side down the table as well as up, and a little observation of the ball when hand-actuated in its spin, reveals exactly how such strokes should be treated.