wee bit simple-could somebody please explain what the difference is meant by the pitch size .
i.e.compare 0,28 to 0,24 which is best picture. which would you buy?

In 'standard' monitor tubes, the dot pitch is the distance between two pixels of the same colour, measured in mm. In aperture grille tubes (Trinitron, Diamondtron), the aperture pitch is the distance between two lines of the same colour (inevitably smaller than a dot pitch, as this distance is horizontal rather than diagonal).
It's not a good measure of quality, if that's what you're looking for, although it's sometimes touted as such. Smaller monitors will usually have smaller dot/aperture pitches than larger ones.