Tim, You are right. Most sources have published 10% to 15%. Sherline recommends 12% to 15% - not sure if that is the same source that you were thinking of. That said, most of the research that I have done suggests that it is better to be closer to 15% than to 10%. And I support that based on personal experience. Having a range that starts at 10% suggests that 10% is OK, but I think having that asks for a bit of trouble. I have been recommending 13% to 15%, but I would also agree with the 12% to 15% range.
