'Turndown ratio' is a flow measurement term that indicates the range a specific flow meter, or meter type, is able to measure with acceptable accuracy. It is also known as range-ability. It is important when choosing a flow meter technology for a specific application. If a gas flow to be measured is expected to vary between 100,000 m³ per day and 1,000,000 m³ per day, the specific application has a turndown ratio of at 10:1. Therefore the meter requires a turndown ratio of at least 10:1.