Mobil 1 0w40 is 3.7 cP (3.7cP * 1/.85 specific density = 4.35 actual HTHS in cSt; using the estimate of 14 * .322 yields an estimated 4.50 HTHS, which is off by only 3.4%). If there is a ~ in front of the HTHS, then it’s estimated by taking the viscosity at 100C * .322 (this conversion has an R^2 value of 94%).