Sergey Kamenshchikov PhD / Senior analyst at IFC Markets | Charles Dow postulates assume that a price of a trading instrument reflects all fundamental data instantly. However market efficiency may be preserved partially due to inertial properties. In this case a trader has to take into account related markets when opening a position: network effect arises. Below we represent a plain FX D1 trading system based on two currency indexes and classic ParabolicSAR indicator. After indexes are incorporated in a single platform a trader obtains an opportunity to analyze EUR/USD currency pair, EURi and vs USDi simultaneously at one screen and one time frame. A conservative trading idea is simple: EUR/USD long (short) position should be opened if EURi and vsUSDi give bullish (bearish) signals simultaneously. If inconsistency occurs and signals of two indexes differ then the opened position should be closed immediately. This strong signal shows us inefficient market stages when all players move as a whole. Our hypothesis is that this property may be used for effective trend following.