Indeed nithi is correct about stamp no. which is a numbering system used for identifying welder's differnt parameters like repair percentage, reporting welds done by a welder for penalties which shall be made for rejected NDT results and so on. clock no. is used for specifying location. as clock's number we assume those number on our pQR sample. for large diameter pipes at least two welder do welding simultaneousley to balance effects of distortion of welding from one other side for example one start welding from 6'o clock to 9'o clock and the other start welding from 3'o clock to 12'o clock. also some Properties of weld metal is different in specific clock, for example at 3'o clock on 5G position, charpy impact test results are the least ones due to maximum heat input.