Load-following resources are used to manage fluctuations in system loads over a longer time period than frequency regulation, typically five minutes. Every five minutes, the system operator managing the load following evaluates the load/generation balance and determines whether currently operating units need to be ramped up or down. Load-following resources are used in conjunction with AGC units to keep the system balanced across each hour. Typical load-following resources include hydropower, gas combustion turbines, gas combined-cycle turbines, and gas or coal steam turbines.