ABSTRACT
Diagrams typically form only part of a wider instructional system and, in order to contribute effectively to that system, they need to be well integrated with its other components. These other components might include such things as:
printed text
a spoken commentary or sounds
photographic images (still or moving)
real objects or situations
a live instructor
other learners
various devices that permit learner input (such as a mouse or touch screen on a computer).
