It is a Churchill Brake Test Meter.It had 3 adjusting screw feet and a spirit level. It was placed in cab, leveled and a card was placed inside the curved spine. Remove cover from pen,mounted on a weighted ,swinging pendulum, and drive off. At about 20-25mph brake sharpley and the weight of the pendulum marked a line up the card showing braking efficiency as a percentage. The pendulum could also move L/R to show if brakes were pulling.
These are older than the Tapley Decelorometer type but were favoured over the Tapley as they gave a physical record of what the brake performance was, rather than relying on testers honesty with Tapley. These were still in use late 90`s early 2000`s as the Army couldn`t procure enough Turnkey meters (Digital Decelorometer) and while they were doing that, everything changed over to RBT anyhow.(Believe this was during paranoia about brake fluid changes not being properly recorded in section 3, and other anomolies that VOSA wern`t happy about)
Useful as an interim test but how legally valid the results are is open to question.
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