IMHO I would be a little wary of gym scales.

A) they get hammered to death
B) unless you use a towel/footwear/kit that weight exactly the same to the gramme you're adding another variable
c) unless you weigh in at exactly the same time to the minute(unless it's the first thing you do on Weds. morning) there's another potential inconsistancy
d) verucas

FWIW a cheap set of digital scales(easier to read as theres no needle to wobble around) put in the same place on the floor at home (preferably sans carpet), in your birthday suit first thing on a weds. morning offers best consistency.