I was wondering if there is a standard way measuring SSS in comparison to objects in the real world like the index of refraction measurements. I know that scale plays a large role in its appearance and intensity but it has to be estimated visually on trial and error. Is there some sort listing of comparisons of the types of material with SSS measurement, such as 'wax=1.000' or 'skin=0.541'or is it better to guess the amount?
I would recommend to base your values on observation instead of guessing. since it's hard to get measured data for something as basic as albedo values, I think it is safe to forget about SSS measurements even if they existed. Correctly exposed and white balanced photographs in similar lighting conditions to your 3d scene should be a really good source of information.