This part of ISO 789 specifies test procedures for determining the lifting capacity of rear-mounted three-point linkage systems: a) the maximum vertical force which can be exerted by the hydraulic lift at the lower hitch points throughout their full range of movement; b) the maximum vertical force which can be exerted by the hydraulic lift, at a point 610 mm to the rear of the hitch points on a frame attached to the three-point linkage, throughout its full range of movement; c) optionally, the ability of the lifting system to maintain the load in the lifted position without hydraulic power. NOTES 1 To ensure that the lifting capacity and the hydraulic power are adequate for effective practical use and also to allow for variation in the performance of nominally identical tractors, the measured maximum performance is reported as that which would be obtained with the hydraulic fluid pressure maintained at 90 % of the pressure sustained by the relief valve (see 6.1.3.4). 2 A static test provides an adequate comparison between tractors. It should be recognized that the test results are to be used only as a means of comparing tractors and not as a way of recommending the size of an implement which can be carried by the tractor.