It has been said that the conductor's most important responsibility is to get everyone to start in time. But that's only the beginning in more ways than one. The actual performance is a small part of the job. Both engineer and contractor, the conductor realises every detail of a blueprint, namely the score, in rehearsal. The conductor determines tempo, adjusts balances (taking into account the tricky acoustic difference between what is heard on the podium and in the hall), shapes musical phrases, regulates dynamics, monitors intonation and, of course, keeps the orchestra together. In performance, the conductor is then that other kind of engineer, driving the freight train of sometimes 100 or more players, all of whom have musical minds of their own.
There is a grammar of conducting, techniques for giving the upbeat, marking time and cueing players, some of whom may do nothing for long stretches and then must come in with split-second precision. But how that is done is personal. Every conductor uses his or her body differently, has individual ideas about eye contact and the choreography of physical expression.
And then there is the extra-sensory perception of conducting which goes beyond intellectual, technical or musical accomplishment. The conductor makes no sound, but the best conductors have their sound, something that can be communicated simply by their presence on the podium (or, in some cases, without the podium). The resultant group psychology has yet to be explained by any of the sciences: the soft ones, the physical ones or even the mystical ones.
The baton makes no sound yet can generate the loudest and most varied sounds in all unamplified music, wielded in a way that 100 or more musicians will instantaneously understand. Yet every conductor does it differently. Typically held between the thumb and first two fingers, batons can be stubby or long. Handles come in varying shapes, often designed by the conductors themselves. The baton, colloquially called a stick, is commonly made of various types of wood or graphite and was first used in early 19th-century orchestras primarily to mark metre and tempo. Today's conductors also employ the baton to convey expression, and a few have been known to get carried away and stab themselves with its sharpened end.