The advance of plasma-display technology speeds on, and the Pioneer PDP-501MX is at the front of the line. This is the first plasma monitor on sale in the United States that is capable of displaying high-definition images, making it the world's most advanced, commercially available product of this type.Squeezing almost 1 million pixels into even a 50" display (measured diagonally) is quite an accomplishment. As soon as I pulled the unit out of the box and set it in its unobtrusive tabletop stand, I connected it to Panasonic's high-definition tuner box and fed the monitor an over-the-air HDTV signal. Without so much as a hiccup, the set accepted the 1920<I>x</I>1080i signal and displayed a bright, clear, sharp picture that made me smile. All this from a <I>big</I>-screen set less than 4" thick!