So I'm wondering if Blackstone still uses the same PC test method they did back 8~9 years ago? Jim Allen had a post in one of those threads explaining their PC test methodology. Sounds like back then at least they didn't use any kind of actual particle optical counting devices like used in the ISO 4548-12 test. Not sure what Blackstone uses these day to do PC testing.
They are using a laser APC which is calibrated by the manufacturer periodically. This changed in 2016 from the old pore blockage method.
Counts are reported per ISO 4406 cumulatively. Unless requested otherwise by the customer.
They sent me quite a lot of information which I will digest...