When congregation concentrating on the presenter or screen, some emergency matters could be happened, to avoid interrupting the presentation, you can display some pre-prepared message on the screen.
Normally the emergency matters could be: -
1. Somebody car is blocking traffic, you have to broadcast this message to congregation so the car owner can re-park their car;
2. Power failure during presentation, you have to inform congregation still remain seated and be calm down;
3. There are a lot of noise during the presentation, you have to educate congregation to be silent;
4. This is bad, somebody step in with dog shit... you have to inform congregation to check their shoes whether they brought in the shit and quickly wash it in washroom.
All these can be easily achieved by using Microsoft PowerPoint, you just need to stand by with the power point file or template, when the above instance happens, you just need to open the file, select the slide and click slide show to display the selected message.
(The clip arts in the slide show are get from Microsoft PowerPoint 2000)