P1110 is a 21" monitor?

I was just noticing something concerning my monitor, after not giving it a second thought for 4 years. When I bought my system from Dell in '01', I had ordered a 19" monitor, but I noticed the monitor they sent was a P1110. I double checked this with my original order sheet, which lists the monitor ordered as a P991 19" (17.8" viewable). I also measured my screen diagonally, and it's 19.8" (viewable). Did Dell send the wrong monitor?....and is the P1110 Ultrascan a 21" monitor?...(if it is, then this was definitely a good thing!)

I would just be curious to know how Dell could have made this mistake......unless it was done for some other reason.