Each line represents the power of a currency: GBP: red, USD: green, EUR: Blue and JPY: Gray. Signals can be generated when currency strength lines cross each other. For example: One could go long when EUR line crosses the JPY line from below. EUR gets stronger while JPY gets weaker. Result would be buying EUR/JPY pair.
Currency Power Indicator Chart Example (EURUSD H1)
Platform: Metatrader 4
Indicator type: Measuring trend strength