R ratio (Q3/Q1)

The ratio of permanent flow rate to minimum flow rate, written as R followed by a number, such as R80 or R160. The values come from a fixed series in ISO 4064 and OIML R 49. A higher R means accurate measurement down to lower flows for the same Q3, and the value can differ by mounting position.

R tells a buyer how well a meter captures low flows, where under-registration tends to happen. Compare R values at the same Q3 and in the same mounting position.