Blackstone Viscosity vs SAE J300 Viscosity

[SubLGT]

Why does Blackstone viscosity differ from viscosity as defined by SAE J300?

On my UOAs, and UOAs posted here, I have seen:

Blackstone assigns to PP 5W-30 a 100 degC viscosity range of 9.1 - 11.3 cSt.

Blackstone assigns to M1 5W-30 a 100 degC viscosity range of 8.8 - 11.1 cSt.

Blackstone assigns to PP 10W-30 a 100 degC viscosity range, of 9.9 - 11.9 cSt.

Blackstone assigns to M1 0W-30 a 100 degC viscosity range of 8.8 - 12.2 cSt.

On the other hand, SAE J300 defines a SAE30 oil as having a 100 degC kinematic viscosity (ASTM D445) range of 9.3 - 12.49 cSt

Why the discrepancy between Blackstone and SAE?
And why does Blackstone assign different viscosities to M1 5W30 and PP 5W30?

 

[CATERHAM]

Have you asked Blackstone?

 

[rslifkin]

SAE specs are for new oil. My guess would be that Blackstone's range is what they would expect that particular oil to be after use. Not all oils of equal weight will get the same numbers from Blackstone, as some have a little higher or lower starting visc, some are more shear prone, etc.