The Allington Suspension Bridge has to be constantly monitored for stress fractures as part of the Bridge safety. As well as having a main stress level reader within the control room, hand held stress readers are used by the engineers for closer inspection.
In Day of Disaster, neither hand-held nor control room readers picked up on the damage caused by a storm, which proved to be disastrous when the Martian Space Probe tried to cross the bridge.
Control room reader.
Chuck using a Stress Reader.