DefiantDandelion on Nostr: My guess would be that labs would measure volume of the original sample, then use ...

My guess would be that labs would measure volume of the original sample, then use something like a centrifuge to isolate and concentrate the swimmers. Then sample the concentration and dilute it with a specific volume of fluid, to decrease the density to something that is finitely countable. Then count, and multiply by the appropriate volumes to get to a count that is average per ml of the sample.