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Hmmm. Because SAE wts relate to viscosity but only if you know the temperature.

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What is the SAE temperature(in Farenhiet SP?) used for there specs? I know what the FAA and SAE standard atomsprhere specs but not the oil temp. specs for viscosity testing

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On the left of side of Widman's pages he has a table of the SAE J300 specifications of viscosities for the various grades. You do have to convert to degrees F but thats not too hard. Just remember 100 C = 212 F and 0 C is 32 F and if you want to do the math its deg C x 1.8 than add 32 F.
http://www.widman.biz/English/Calculators/Graph.html

When get an oil spec sheet or send a sample out for analysis, they provide the viscosities of that specific sample or product because there is an allowable range within each grade. Widman has some graphs in his pdf on oil for corvairs/flat tappet engines. He explains the various properties of engine oil far better than I could and for that alone it is worth downloading.

Nemesis. Viscosity is a physical property. The SAE weight system is way to classify a useable product for our engines. J300 specifies the range of viscosity characteristics allowable within each weight grade.