The use of differential pressure as an inferred measurement of a liquid's rate of flow is well known. Differential pressure flowmeters are, by far, the most common units in use today. Estimates are that over 50 percent of all liquid flow measurement applications use this type of unit.
Between 1% and 15% of people globally are affected by kidney stones at some point in their life. In 2013, 49 million cases of occurred, resulting in about 15,000 deaths. They have become more common in the Western world since the 1970s. Generally, more men are affected than women.
In the US alone, the NKF estimated in 2002 that 20 million people had early chronic kidney disease and did not know it, and another 20 million faced an above average risk of developing it. Screening for chronic kidney disease has been generally neglected and is of inestimable value.