ditto on what dragonchilde said. Take a few min and go through your weigh ins and change them to the number they should have been; the tracker will change accordingly.
Better to know your real weight than be lulled with false underestimations.
I think my scale is bad as well (its a cheap plastic thing; if I move it a foot one way or another I magically lose/gain a kg or two -_-; )... I'm getting a nice one with a fat % guesstimator (though I still think they can't *really* tell that) and so on once I go home in mid Feb.
I don't doubt I'll be shifting my values as well.
| current weight: 151.0