Steam engine indicator made by Crosby Steam Gage and Valve Company

Steam engine indicator made by Crosby Steam Gage and Valve Company, Boston. Date made about 1895. Recording drum 900mm x 460mm diameter

Steam engine indicators were used by the mill engineer to monitor the pressure inside one end of the cylinder. Paper would be secured around the drum and the rotating drum is attached to a moving part of the engine with a piece of string. As the engine runs, the paper is rotated under the pressure indicator's pencil, causing it to draw a line as the drum moved back and forth, creating a visual representation of the pressure inside the cylinder during one complete stroke of the piston.