You could do that, but if you're trying to set standards, you have to take into account your ability to measure these things reliably and accurately. (It doesn'

You could do that, but if you're trying to set standards, you have to take into account your ability to measure these things reliably and accurately. (It doesn't do any good to set standards that nobody can conform to because their equipment is never sensitive enough to use them.) Can you measure a liter more accurately than you can measure a kilogram of some reference material?