[De'vID]> Can ler be used to mean "oscillate", like for a usual pendulum (with the pivot at the top)? Or is it only used when the pivot is at the bottom? Also, would a regular rhythm like that of a metronome be described as lerchu'?

Yes. ler can be used for "oscillate," and it can be used for a pendulum regardless of whether the pivot is at the top or bottom (or somewhere else). And lerchu' could be used for what a metronome does. Maltz was glad you asked these questions, because they reminded him of another word (and helped clarify the meaning of this one). The other word is lav, which can be translated "lean, incline, slant" and so on. It means something like "move to a slanted or angled position." The starting position is often, but doesn't have to be, upright or perpendicular. If it's a person, the person's feet stay put (as with ler).  And, as with ler, the pivot point can be on top (or somewhere else). The difference between ler and lav is that ler is used for continuous swinging, back and forth and back and forth (forward-back-forward-back, etc., or left-right-left-right, etc.), while lav means motion in one direction only, then the motion stops (though the stop can be very brief). Returning to the upright (or earlier) position is lavHa'. For both ler and lav, the direction of motion doesn't matter (left, right, forward, whatever).