The art of presentation
Until the middle of the last century, speakers of a lecture or other presentation had no other visual aid than facial expressions and gestures, and, mainly for scientific lectures, chalk and blackboard. It is a fact that for most listeners the visual impact is important for better understanding and long-term memorization. The presentation technique evolved and slide projectors were installed in almost every conference room. But the production of slides were expensive in time and money and slides had one major disadvantage: often too much information were displayed at the time a slide was shown. To obtain a synchronization between spoken word and displayed picture, a slide should contain only few items. The balance between spare information and pretty layout was difficult to obtain.
With the widespread of overhead projectors in the sixties and seventieth the main problem of slide-based presentations was circumvented: The production of the transparencies was quite simple (in the beginning most of them were hand-written), and to obtain the synchronization a simple trick was used: An opaque sheet layed on the transparency hides the bottom part and the speaker can pull it down step-by-step as the presentation goes on. This was a very efficient and simple kind of animation.
When personal computers became available in the eighties, they could be used to replace the hand-written transparencies with pretty computer-generated graphics printed on a transparency. The presentation trick remained the same. Only when video beamers became affordable in the ninetieth, the overhead projector became obsolete and the computer screen containing the visual information is displayed in real-time to the audience.
To simplify the creation of computer based screen-slides, an application software is appropriate. Microsoft's Powerpoint became a quasi-standard, but other products are also available (like OpenOffice Impress). In order to visualize the slide step-by-step an animation tool is used. This has a major drawback: while preparing your presentation, you have to schedule with great care the appearance of all animated items. And, when giving your lecture, you have to remember this scenario even if your preparation has be done weeks ago.
Lazy of animation tools
It is not only nostalgia to reinvent the hiding sheet from the overhead projector era. It has the distinct advantage to let you hide and show items interactively at the time of presentation. But instead of a real sheet moved by hand, you move a colored, opaque or semi-transparent borderless window by dragging it with the mouse. This small, but useful presentation utility is called CoverSheet. Just have a look at the following demonstration: