Post Production Pros commonly run their systems locked to a reference signal such as "black burst" or "house sync" so that all machines in the studio (audio or video) are referenced to the same "master clock." When a system is locked in this way, and you trigger to start at a specific location, your system remains locked all devices are running at the same speed. The term "resolved" refers to this kind of lock. In a "resolved" digital audio system, the speed of the "slave" audio system is constantly and subtly adjusted to match the "master." Pro Tools LE *can* be resolved to an external clock via the S/PDIF port on the Digi 001 or AMIII, but external sync boxes that can do this (available from third-parties) are pretty expensive. Without a resolved system, you cannot maintain lock over longer periods of time to analog tape transports (like cassettes, or even multi-track machines). The choice about how far to go with resolving your system lies with your needs and budget.