For example, you may want to know what the rate of change is in a price. If you are focusing on momentum, you may want to know what the rate of change was in momentum between two quarterly earnings. The rate of change can bring telling signs about a company or how price is reacting to certain conditions.
There are many different aspects of the market you have to monitor, whether it be investing or trading. The rate of change ratio is in regards to momentum. This is typically how quickly there is change over a period of time.