Elder Ray (Bear Power)

Developed by Dr Alexander Elder, the Elder-ray indicator measures buying
and selling pressure in the market. The Elder-ray is often used as part
of the Triple Screen trading system but may also be used on its own.
Dr Elder uses a 13-day exponential moving average (EMA) to indicate the
market consensus of value. Bear Power measures the ability of sellers to
drive prices below the consensus of value. Bear Power reflects the ability
of sellers to drive prices below the average consensus of value.
Bull Power is calculated by subtracting the 13-day EMA from the day's High.
Bear power subtracts the 13-day EMA from the day's Low.
You can use in the xPrice any series: Open, High, Low, Close, HL2, HLC3, OHLC4 and ect...