[hammock]

Exactly. It allows for less-precise (i.e. more variability) chip size, not chip scales. :)

Simplifying the scenario might clarify what's happening. Imagine any given chip could weigh 1-2oz. And you are trying to fill a 2oz (minimum guaranteed content) bag. You already have 1 chip in the bag, weighing 1oz. The next chip you add (think "marginal" from econ class) weighs anywhere from 1-2oz and could tip the scale all the way up to 3oz, when you are only looking for 2oz in the bag. But if you use two scales, you have now a choice of TWO chips to put in the bag, so you pick the one that weighs closest to 1oz. And ultimately this allows you to fill more 2oz bags with the same quantity of chips.