I'm unable to eat enormous quantity of foods, on diet or off diet. Usually 150-200gr of carbs is pretty much what I can take in one sitting, so yes it should not change my weight that much, if all carbs are stored with it's water, it should make add about 1lbs to 2lbs tops.

About the scale yes, it's extremely precise, even though I weight myself 3-6x every time, all the same, I tested thoroughly, I've tried to put the weight in front, back, leaning every way, it always come back to the same weight, some time also I do make it 'forget' my weight by grabbing a furniture and adds lots of weights or remove some and it come back to the same decimal.

Eric