One of the most profitable strategies I've seen goes like this:
Current GBPJPY minus "Center" GBPJPY says "What would the GBPJPY profit/loss have been if I had bought GBPJPY at the Center GBPJPY exchange rate?"
"Center" EURCHF - Current EURCHF says "What would the EURCHF profit/loss have been if I had sold EURCHF at the Center EURCHF exchange rate?"
The sum of the two results is what we call our shadow profit (tip of the hat to Forex Assistant associates).
If the shadow profit is negative we buy GBPJPY sell EURCHF. If the shadow profit is positive we sell GBPJPY buy EURCHF.
The positive or negative levels to enter are values like 75 150 250. The market appears to VIRTUALLY ALWAYS swing toward the other side where the shadow profit is positive or negative opposite of what it was before.
One big key is having reliable "Center" values for the two currency ps. It appears that taking an SMA of 60 four-hour bars' highs lows works pretty well. The shadow profit (deviations) represent trade entry opportunities.