Tomas,
Assuming your dielectric is read in somewhat of a controlled environment (ie Temperature) that should fix the viscosity vs. dielectric issue. However the larger task at hand is knowing exactly when the dielectric is at the point in which it needs to be changed. I have done a lot of research on this subject, and I have seen alot of different numbers out there, any where from a .2% change to a 15% change in dielectric. This is why it takes alot of testing and research to determine exactly when this dielectric reaches the point to where you can say your oil has degraded. I do not think you will get anyone to tell you what that percentage is, as that is the kind of info companies can sell.....There are a few oil quality sensors out there on the market that use dielectric to determine oil quality but like I said they already did the research and testing so that they can use that information to sell their product. If you do get this information from someone or some company feel free to share it!!!! Good luck.....