Here is something for you to remember: "The earlier in the stroke you
cut off the greater the economy, but less the power; the later you cut
off the less the economy and greater the power."

Suppose we go into this a little farther. If you are carrying I00
pounds pressure and cut off at I/4, you can readily see the economy of
fuel and water, for the steam is only allowed to enter the cylinder
during I/4 of its stroke; but by reason of this, you only get an average
pressure on the piston head of 59 pounds throughout the stroke. But if
this is sufficient to do the work, why not take advantage of it and
thereby save your fuel and water? Now, with the same pressure as before,
and cutting off at I/2, you have an average pressure on piston head of
84 pounds, a loss of 50 per cent in economy and a gain of 42 per cent in
power. Cutting of at 3/4 gives you an average pressure of 96 pounds
throughout the stroke. A loss on cutting off at I/4 of 75 per cent in
economy, and a gain of nearly 63 per cent in power. This shows that the
most available point at which to work steam expansively is at I/4, as
the percentage of increase of power does not equal the percentage of
loss in economy. The nearer you bring the reverse lever to center of
quadrant, the earlier will the valve cut the steam and the less will be
the average pressure, while the farther away from the center the later
in the stroke will the valve cut the steam, and the greater the average
pressure, and, consequently, the greater the power. We have seen
engineers drop the reverse back in the last notch in order to make a
hard pull, and were unable to tell why they did so.

Now, as far as doing the work is concerned, it is not absolutely
necessary that you know this; but if you do know it, you are more likely
to profit by it and thereby get the best results out of your engine.