When designing slides always remember to design for the last row. Make sure that whatever it is you are showing on your slides is big enough to be seen from the back of the room. If you have text on your slides, make the font size big enough so that it can easily be read from the last row. There is nothing worse than being in the back of the room not being able to see what is on the slides being presented. So remember to make it BIG.
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Image Credit: OeilDeNuit