Inverse versine

Inverse versine is a way to measure how something changes over a period of time. It is kind of like measuring a change in your height-- if you're 5 feet tall and you grow a foot, that is a big change! But if you become 6 feet tall, that is less of a change, because it's only one foot. Inverse versine is a way to measure how much something has changed relative to its original value.