Way back, when I was first learning about HTML programming, the rule was (and still should be) to program for the least common denominator, as far as the equipment viewing the page goes. At that time, it was 640 x 480 screen resolution.
Lately, I've been thinking about something. With my new computer setup, I've been adjusting my photos according to how they look on my (quite beautiful) calibrated monitor. This is great for print, but looking at my other monitor, which is straight out of the box, basically the same thing everybody else has; my photos are significantly lacking. Does this mean I should be doing everything twice, the first for print on my good monitor, and again to the other one for online viewing?