The invention relates to cyclohexenone derivatives of benzo-condensed, unsaturated 5-ring nitrogen heterocycles of general formula wherein X represents N or a group CR3, Y represents O, S, SO, SO2 or NR4 or XY represent SN and X represents sulfur, and the variables R1, R2 and Hex have the meanings given in claim 1. The pet restriction device comprises an entry panel, at least one door located on the entry panel and comprising a door axis, and a locking device. Gating the PLLs, however, has been difficult because of the usual requirement for a separate clock for control logic and because the PLL requires timed to reacquire phasefrequency lock. The system determines whether a connection has been properly tightened by sensing the torque and angular displacement of the connection as it is being tightened, and comparing the data to a stored reference set of data or curves.