SXAA-BB-C where:

AA = original consumption of replenisher in liters per hour based on a daily average
BB = electowinning capacity in kilograms of copper plated per hour
C = number of etchers support (not always used)

therefore, an
SX50-7.5-2 has the capacity to replace the consumption of 50 liters per hour of replenisher while plating 7.5 kg per hour of copper and can simultaneously support two etchers.