The scoop needed to be lowered at speed at the correct location – shortly before the start of the trough – and raised again when either the tank is full, or at the end of the trough. Failure to raise the scoop promptly when the tanks are full would resulted in large volumes of water being expelled from the vents, soaking the tender and footplate. The fireman therefore had to observe the water level indicator (a float in the tank, connected to an external pointer) carefully and be poised to retract the scoop as necessary. Lineside indicators were provided to assist engine crews in determining the location; in the UK it was a large white rectangular board with a black horizontal zigzag marking. On American railroads, illuminated trackside signals were employed for night-time usage, to indicate the start and approaching end of the track pan.