The advantage of this formula is that it only has two constants and therefore we only need two sets of data to solve for the constants A & B, usually the 40 and 100Â☌ points. This is the formula behind online calculators and the straight line graphs of log log data.
T is the temp in Kelvin and A & B are constants unique to each oil. The "standard" calculation of the variation of oil viscosity is based on the ASTM-Walther formula. But there have been warnings that the formula cannot be relied upon.Įxtrapolation is usually done with the help of online calculators and Apps for your phone or tablet. In order to pursue Harman index, etc, calculations, the first step is to extrapolate the viscosity data to 150Â☌.
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