Most ergonomic way to present text info on iPhone

What is the best and most ergonomic way to present info on an iPhone?

I currently have a simple GPS-type app that on one view shows the map and on another all the movement data such as speed, altitude, heading and co-ords. I show these few variables (which are constantly changing) with white font on a black background.

The font I currently use: Helvetica, 24.0

This app will actually be used in driving conditions so i开发者_JAVA百科t has to be good on the eye and readable in many conditions, e.g. at night. Obviously it will be readable, but what is the most ergonomic option, looking at these aspects:

• Font Family (AKA Type, e.g. Helvetica)
• Font Color
• Font Size
• Background Color

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I've found that white on black works very well on these displays. For one thing, it makes the whole phone one solid black area (if the phone is black), and the text stands out at a glance. I would consider using Helvetica Bold rather than Helvetica. But I think Helvetica is a good choice because it's the standard on the iPhone, and people will expect it. As for font size, with a GPS I'd much prefer text to err on the side of being large than being small. People will forgive a little cramping in the map display if you give the text a size boost.