I work for a company that produces (among other things) a microbalance that can measure mass/weight from around 100ng to 100mg ie it is accurate over 6 orders of magnitude. However, this relies on gravity acting as a counterforce to a computer controlled magnetic field.
Has anyone created a technique that can measure mass over such a wide range in freefall (zero G)? What do they use on the ISS? The only method I can imagine would be something involving vibration and/or springs, whether micro or macro.