The present invention relates to an improved level wind arm for a winch drum assembly, and a winch drum assembly incorporating such a level wind arm. The monitored test block includes various safety features to prevent damage to the equipment or harm to a technician. In addition the compounds can be labeled with technetium and rhenium isotopes using known chelation complexes. A control valve is movable relative to the first valve opening to regulate fluid flow through the first opening when fluid flow is in the inlet-to-outlet direction, and is movable to engage the first valve opening to restrict fluid flow in the outlet-to-inlet direction. The seal length L1 of the flow guides and the seal length L2 of the overlapping section are substantially the same. The determination may be based on the correlation values.