I found this posting on another website:
Both ROTELLA T SAE 15W-40 and ROTELLA T Synthetic SAE 5W-40 have HTHS numbers exceeding 4.0, well in excess of the SAE J300 minimums of 3.7 cP for SAE 15W-40 and 2.9 for SAE 5E-40 grades. Please don’t get stuck on high-numbers-are-better, though. These are bench test numbers. Just like TBN, more important is performance in an engine, where how well oil viscosity stands up to shear stress (or TBN to acids) would be a better measure than how high the new oil numbers is.
Both ROTELLA T SAE 15W-40 and ROTELLA T Synthetic SAE 5W-40 have HTHS numbers exceeding 4.0, well in excess of the SAE J300 minimums of 3.7 cP for SAE 15W-40 and 2.9 for SAE 5E-40 grades. Please don’t get stuck on high-numbers-are-better, though. These are bench test numbers. Just like TBN, more important is performance in an engine, where how well oil viscosity stands up to shear stress (or TBN to acids) would be a better measure than how high the new oil numbers is.