Just to clarify SAE viscosity numbers: (and to rant a bit)
The numbers on the scale are relative and are don't correlate to an actual measurement, similar to the Fahrenheit temperature scale; 80*F doesn't mean anything other than it is cooler than 90*F. You can almost think of it as a rating or range of viscosity. It could be Aw-B, or 2563w-5632, or extra-light w - light and have the same meaning.
The Xw (i.e. 0w) means the oil flows similar to a SAE "Ow" (bottom of the scale) viscosity when cold. The -XX (i.e. -20) means it flows similar to a SAE "20" when hot. It does not mean the oil is "thinner" or "lower weight" when cold or "thicker" or "higher weight" when hot, quite the opposite is true.
This is also confused by having seperate engine oil and gear oil scales on the SAE chart. SAE 75w gear oil is not "thicker" than SAE 50 motor oil, in fact SAE 75w gear oil is about the same viscosity as SAE 10w to 20w motor oil. Similar to the Fahrenheit and Celsius temperature scales, 212*F is not "hotter" than 100*C, they are the same temperature.
The "w" stands for "winter". I don't know why this is added to multi-grade oils but it is one more area of confusion in the SAE system.
The ISO scale on the other hand does correlate to viscosity and only has one scale. An ISO 32 oil has a Kenematic viscosity of 32 at 104*F, measured the same way as they do in the SAE system. It doesn't matter if it is turbine oil, way oil, gear oil, etc it is always ISO viscosity 32. ISO 64 is always more viscous than ISO 32, they are on the same easy to understand scale. ISO 32 is about the same as SAE 75w gear oil or SAE 10W engine oil.