The Robert Sorby eccentric chuck weighs 5.1/2lbs (2.5kgs). This is designed to counterbalance the weight of the workpiece when offset. This gives far more stability than other systems where both the chuck and workpiece are offset from the centre which can lead to damage or potential injury, Fixing is so secure that a tailstock is not always necessary. There are three fixing methods – faceplate, screw chuck and ball drive and socket. 
The unique eccentric boss is marked 0 to 35 on its outside diameter. These marks represent the amount to which the workpiece held in the boss can be off set from the central axis. When set in 0 the workpiece will run concentrically. When located on any other mark in the window you are shown the amount of off set from the central axis. 
Clear markings ensure not only that dimensions are accurate but also that they can easily be repeated. With any off-centre project all preparation of markings and locations is critical.