Improved techniques for making copy detection patterns and using them to detect copying relationships between digital representations. A trigger mechanism for releasing the mandrel to cause the hammer surface to impact the anvil surface includes a trigger sleeve axially positioned with the housing and a collet that engages the mandrel during application of a load to the mandrel. The control circuit obtains an integral quotient value x by dividing by the number n the sum between the detected numbers for the first and second numeric value data, to stop the clock pulse supply to a particular number x of flip-flop circuit counted from the lowest-order. The presence of the watermark is then detected by a cyclic sliding correlating.