Jill, Sometimes a good back up plan can save the day. For instance, when all the computers are down (or the LCD projector). Technical things like the copiers out of whack, computers, overhead - anything electrical, that can create a minor emergency. But a good back up plan that doesn't rely on anything electrical that's low tech, easy to implemment, and related to the topic can fill the period and not waste students time. Maybe a review, a discussion, reading from the text, all simple but useful ways to assist when things go awry. Barry Westling