I just got the replacement for my Treo 270 which had speaker problem

I noticed that the optimum screen setting is very different with my previous unit.

My old unit, the optimum setting (most readable screen) for contrast and brightness were both somewhere in the middle bars.

But my new unit to get the optimum setting, the contrast has to set to almost minimum (left side) and brightness to almost max (right side)

What is your optimum setting for contrast and brightness?

Wondering why the variation between one unit and the other is so wide?