Equipoising support apparatus

A support arm comprising:

• a first parallelogram linkage having a first end and a second end, the first end connected to a first end block at a first pivot, the second end connected to a second end block at a second pivot;
• a second parallelogram linkage having a first end and a second end, the first end connected to the first end block at a third pivot, the second end connected to the second end block at a fourth pivot;
• a resilient member pivotally connected at a first end to a bearing shaft, the bearing shaft disposed between a top bearing block and a bottom bearing block, both bearing blocks moveably attached to the first end block, the resilient member adjustable along a termination path coincident with the bearing shaft, the resilient member having a second end connected to the second end block at the fourth pivot, thereby biasing the first end of the first parallelogram link with respect to the first end of the second parallelogram link
• wherein the angle of the resilient member termination path with respect to a substantially vertical line is adjustable at least in part by a force modification device;
• and
• wherein the force modification device causes the resilient member termination path to be adjusted dynamically in response to movement of the parallelogram linkages.