pH is one of the most often calculated and measured properties of solutions, products and substances. When in 1936 Arnold Beckman was readying his first commercial pH meter, total global demand for such a device was estimated for 600 pH meters over 10 years before the market saturation. Year later global demand had to be reevaluated, as first year sales reached 444 pH meters (see pH meter history)!
pH is so important as it can drastically change equilibrium state and speed of many reactions. Many plants tolerate only narrow pH range of the soil. Small change in the pH of blood can be fatal for any animal. Precise control of pH is vital for good yield in many industrial processes - and so on.