PortafilterProcrastinator you just put 10.0g of coffee in & shake for 2 min.
There’s not much more to really understand. The % that falls through 400 or 500 Kruve is a good guide to what the grind setting is relative to a given drip recipe.
But, Kruve holds 2 sieves. If your upper sieve is too small (like using 400 & 800 for instance) you won’t catch enough of the ground weight to give any insights into the overall view on the distribution (400 & 800 usually only traps 20-30%), you are then just wasting an opportunity.
To capture something vaguely useful, you want to trap a decent amount of the weight, either side of the average size, historically with ASTM/ISO you would use 2 sieves to catch around 68% (might be 65%, might be 75%, but roughly +/- one standard deviation around the mean in the distribution). To do this, your sieves with Kruve need to be x2.5 to x3 in mesh size apart. This isn’t so important in terms of identifying a grind setting, but helps identify/compare grinders with narrower or wider distributions. It just adds little more interest/value to your sifting for the same amount of work.
For example, with a Hario, or Porlex 400 & 1600 will catch around 68% of the grind, but with a tighter distribution grinder you might catch more like 90%, which is still useful, but you could use a smaller top sieve to catch 68% with a tighter grinder. (I generally use 1600 in the top all the time, to start with at least).
I am not saying however that the amount captured directly correlates to an obvious level of quality in the cup, the setting in terms of fineness/coarseness is most critical. Like I said, Kruve has 2 sieves, basically just make the top one big enough to give some interest to the results.