Methods and an apparatus for reducing the effect of background ionizing radiation depression in vehicle and container monitoring systems due to shielding effects from components of the vehicle or container or modifications thereof. The wrench includes a wrench head including a face having an elongate groove extending along a central longitudinal groove axis between opposite first and second ends of the groove for receiving the torque bar. The light source is arranged to emit detection radiation in a wavelength range in which a resist to be used for processing the substrate in the lithographic apparatus is sensitive.