is it possible...

to gain 4lbs of water weight in a day? yesterday morning i weighed myself (pre breakfast and post morning pee) and it said 155. i had a breakfast sandwhich and then a medium coffee from top donut right before i had my physical. when the nurse weighed me on their high-tech scale it said i weighed 159...?! does that mean my digital scale at home (which is relatively new...under a year old) is skewed ? or did i just gain 4lb of water weight?!

Different scale, after eating and drinking while (maybe?) clothed will very predicatably yield a completely separate (and higher) response.

Well you did just finish eating so that might be it . But Your body changes 2.2 pounds through out the whole day . And no i don't think there is anything wrong with your scale just be sure your not kicking it around and stuff and it should be chill .

Breakfast sandwich + coffee + clothes = 4 pound gain.

hahah yeah i was clothed..and actually it wasn't a sandwhich..it was a big bowl of fiber cereal...so i'm going to agree with you all and go with the fluctuating water weight theory. thanks guy!

Even had none of those been a factor, just the fact that it was a different scale means you will be getting a different weight - scales are different. Use one scale at the same time under the same conditions, and you'll get a sense of what your weight is doing (although the trend is more important than an individual weigh in).