Everything is relative.
Checking the uniformity of a beaker's scale is very simple. Pour the liquid up to the first mark, pour it into another container, pour it again, return the liquid from the other container; the level should be at the second mark. And so on.
Now about the division value, which can't be properly adjusted in the apocalypse, but it's not necessary. Everything is mixed up in proportions, and if we need a 1:2 ratio, it doesn't matter at all whether it's 1 liter to 2 liters or 1 pint to 2 pints. The ratio will be the same. Precise scales are essential in modern laboratories, since different people can measure different materials with different instruments. But here, we do everything alone and with one instrument.