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Estimate kinematic viscosity at any operating temperature from two measured data points, using the ASTM D341 Walther equation.
Walther equation:
W(v) = log10( log10( v + 0.7 ) )
W is linear in log10(T) with T in Kelvin: W = A − B · log10(T) From two points (T1, v1) and (T2, v2):
B = (W1 − W2) ÷ (log10 T1 − log10 T2)
A = W1 + B · log10 T1 At the target temperature T:
v = 10^( 10^(A − B·log10 T) ) − 0.7Reference points are 40 °C and 100 °C. Extrapolation far outside this range loses accuracy, particularly below the cloud point.
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