An illustration in your most interesting article on brakes, which was captioned as a Tapley performance meter, did, in fact, show a gradient meter.
The brake testing meter and the performance meter which doubled as a gradient meter were all, of course, virtually the same thing but with differently graduated scales. The brake tester incorporated a ratchet to latch the scale at the maximum reading achieved during the test.
It was the standard brake tester used in the MoT test until quite recently.
JG Millward, Oxford