Cause it’d be “even” if it was 42 or 44.

Sorry, I couldn’t help myself…
Anything other than 30, 40, 50 for a CYA result tells us it came from a pool store, which as you know know we don’t trust as accurate. That’s all that meant. Once you get your test kit, you will fill up the water sample up in increments of 10 until the dot dissapears. Once it does, that’s your CYA value. So there’s no values between the decade numbers. In addition, the FC for CYA=43 is the same as the FC for CYA=50, so there’s no need to know if it’s 43, 47, 41, etc. just need to know if it’s over 40, over 50, etc.