its to do with the research stats.
the Z score is a s a result of a calculation that I wont bother you with, too boring and confundeling.
the percentile is to do with percentages i.e. the 25 percentile refers to everyone under 25% in the research results (sorry, not good at explaining)
basicly arse to it
they change all the time, if baby is growing well, happy and not losing weight then no worries...
