I'm with Briansmum and Judy. The scales the weight readings were taken on were 1) larger scale at vet = more percentage of error, possibly +- 50 grams and 2) the scale at your mothers could have been "tweaked" or out of calibration.
Digital scales use a strain gage load cell. This is, to picture it for you, basically a resistive piece of wire attached between 2 points of a metal housing and it reacts by sending an increasingly larger dc voltage change as the metal deflection between the 2 points it's attached to changes in distance between the two points. The more weight. the shorter or longer the distance depending on the load cell design.
Anyway, if anything too heavy has been placed on a sensitive digital scale or someone has tweaked it sideways, it will "Tweak" the metal housing of the load cell and throw the readings off. Thus a re-calibration is necessary and if it won't calibrate, the scale is now trash.
So, I would not be worried about the weight change at this point. Get a new gram scale and track it's weight daily for a while. :-)<br><br>Post edited by: danmcq, at: 2007/11/23 15:29