The resistance beer encounters as it flows from a keg, through the tap, beer line and other hardware designed into a beer dispensing system. A beer system is considered to be in balance when Applied Pressure equals the Restriction and results in a Flow Rate of approximately one gallon of beer per minute. Restriction in a beer system comes from the type of beer line used and the size and length of that line, the gravity (lift or drop) in the system, the altitude at which the beer is dispensed, and the components used in the beer system. Sometimes referred to as resistance or hold back.