I'm curious why you expect that a system must work across multiple markets to be valid? I didn't say that the system has to work across multiple markets to be valid, but that if the system did work well across multiple markets, it increases the likelihood that the system has successfully captured some underlying characteristics relating to what drives markets in general (fear, greed, etc.). Obviously there are many systems that try to exploit certain characteristics that only exist in a specific market or instrument (such as economic reports for indexes, or crop reports for some commodities). You would not expect a system designed to exploit these specifics to work well across all markets. However, if a system did indeed perform well across numerous markets, then it is more likely that system will continue to perform in the future because it is more likely that system has captured a general underlying characteristics of all markets (fear, greed, etc.) than just specific characteristics (economic reports, crop reports, etc.). This was the case for the Turtle system and Aberration, which was capturing the underlying nature of trends that were prevalent during the 70's, 80's, and somewhat in the 90's.