Sharon, I recommend two scales.
The first, a small unit with a basket or tray for holding piles of stuff or floppy items. It should have a maximum weight capacity higher than the weight of your heaviest item (maybe your backpack or tent?) A commercial digital kitchen scale with a bowl for holding stuff works for me.
The second scale could be your bathroom scale or similar high capacity scale for checking your 'From Skin Out' weight. Stand on it wearing your pack, and then subtract your body weight.
If you are standing there in the store facing a shelf full of choices, put an item on each; if one scale gives an anomolous reading, exclude it from your consideration, it is inaccurate. That technique works well for thermometers, compasses, barometers, etc..
Accuracy is the correctness of the scale, precision is the number of digits it reads out. My bathroom scale requires me to input my geographical location (once of course) so it can compensate for anomolies in gravitational pull! But then it only reads out to the nearest 100 grams.. I find that odd.