What is meant by turndown ratio?

The turndown ratio is a measure of the meter’s working range. By dividing the upper most flow rate by the minimum, measureable flow rate you determine a value that is usually presented as 3:1, 10:1 or maybe 100:1 (pronounced one hundred to one). The larger the ratio the wider the operating range of the device. Meters that cannot hold their accuracy are often specified to work in a 3:1 range. Higher precision devices that hold their accuracy may be specified as 200:1 or 1000:1 devices. Such a large range makes it possible to use the same meter for both 10 L/min measurements and 10 ml/min.