The coding of my app requires me to descend into the detail of font and screen sizes: SlideMagic 2.0 renders slides on the screen (HTML), in PDF, and in PowerPoint. It requires some fiddling to get things to look exactly the same in all three of these channels.
This post by Geetesh Bajaj explained nicely why things can go “wrong” in PowerPoint. Switching from “4:3” to "16:9 onscreen” mixes up all the font sizes. Why? Font sizes are expressed in terms of character height. The “16:9 onscreen” mode keeps the width of the screen, just makes the height smaller. The result, all text looks way too big.
Recently, Microsoft added the “wide screen” setting. This is the one to use. The height of the screen is kept the same, the width is made longer.