The Movement Directional Index (MDI) is an indicator used in the forex market to measure the strength of bullish and bearish momentum. Developed by G.W.C. Higgel, it helps traders identify buy and sell opportunities in a timely manner. It is calculated by measuring the change in price over a specified period of time. The more the amount of change, the greater the value of the MDI. When the MDI is above 50, it signals a bullish market and when the value is below 50, it signals a bearish market. With the help of the MDI, traders can refine and improve their trading strategies.