Oh, I see what you want. Here, I'll get the ball rolling, with... fonts!
Here's a DPI calc formula:
sqrt(w*w + h*h) / DiagonalInches = DPI
An average monitor is likely 96 DPI. I have a 17 inch monitor. According to this formula, it is close to 96 DPI.
Ruler:
sqrt(1280*1280 + 1024*1024)/17.32 = 94.6 DPI
Advertised:
sqrt(1280*1280 + 1024*1024)/17.00 = 96.4 DPI
Close enough. The pandora is 800x480, 4.3" diagonally.
sqrt(800*800 + 480*480)/4.3 = 216.96 DPI
This gives us a 96:216 ratio. Font should be 2.25 times larger to appear the same size on a Pandora.
Now, most people will be slightly closer to their Pandora than to a monitor, so this could be reduced to 2 times larger without much detriment.
In your hand near your face, fonts would still be fairly clear at 1.5x the size on a monitor - but this cannot be guaranteed. A person could be sitting with the Pandora on their lap, or is perhaps using it on the dashboard as a GPS.
This forum has either 14px or 16px fonts. Using all this info, I'll throw together a standard.
CODE
=== Pandora Fonts ===
-Pandora screen is 216 DPI. Most monitors are 96 DPI. This is a 2.25 ratio.
Vertical height:
18px; very tiny
22px; tiny
28px; small - like the "My Controls" at the top of this page.
36px; average - appears the same as the text you're reading right now
48px; headings
72px; really big text
I believe this is correct. Break out the huge fonts!
h34r: