In the Production Vehicle (PV), lasers, vertical and horizontal actuators, gyros and accelerometers measure the interaction of the vehicle passing over the track. Outputs from the measuring system include track gauge, alignment, twist and cant. Other systems on the roof of the Development Vehicle (DV) measure features such as overhead line height and stagger. On the West Coast Main Line, particular care has to be taken to ensure that clearances are maintained for the use of tilting trains. The train captures video footage from the front and rear power cars.