The force index (FI) is an indicator used in technical analysis to illustrate how strong the actual buying or selling pressure is.
High positive values mean there is a strong rising trend, and low values signify a strong downward trend.
The FI is calculated by multiplying the difference between the last and previous closing prices by the volume of the commodity, yielding a momentum scaled by the volume.
The strength of the force is determined by a larger price change or by a larger volume.
[1] The FI was created by Alexander Elder.