Apparatus and method of compensating thermal contraction of a hydraulic system

Apparatus to compensate for contraction of fluid in a hydraulically operated telescopic boom (110), comprising: a monitor (200); and a supply (210) of hydraulic fluid; and fluid control (220) responsive to said monitor (200) to provide hydraulic fluid from supply (210) to a hydraulic device controlling extension of the telescopic boom (110) is characterized in that the monitor is used to determine the elevation angle of the boom (110) and, when the elevation angle exceeds a predetermined threshold angle, the fluid control provides the hydraulic fluid from the hydraulic supply device.