The Rate of Change Indicator (ROC) is a popular and useful Forex indicator that is available for free on the MT4 trading platform. It is used to measure the rate of change of a currency pair over a given period of time. The ROC indicator is calculated by dividing the current price by the price of the same currency pair at a certain point in the past. The ROC indicator is a useful tool for traders looking to identify short-term trends and make decisions based on price movements.