Stoke Bank has a gradient of between 1:178 and 1:200. "Mallard", pulling a dynamometer car and six coaches, topped Stoke Summit at and accelerated downhill. The speeds at the end of each mile (1.6 km) from the summit were recorded as: 87½, 96½, 104, 107, 111½, 116 and 119 mph (141, 155, 167, 172, 179, 187 and 192 km/h); half-mile (800 m) readings after that gave 120¾, 122½, 123, 124¼ and finally 125 mph (194, 197, 198, 200 and 201 km/h). The speed recorded by instruments in the dynamometer car, marks were made every half second on a paper roll moving 24 inches for every mile travelled. Speeds could be calculated by measuring the distance between the timing marks. Immediately after the run staff in the dynamometer car calculated the speed over five second intervals, finding a maximum of 125 mph. 126 mph was seen for a single second but Gresley would not accept this as a reliable measurement and 125 miles an hour was the figure published. Ten years later, at the time of the 1948 Locomotive Exchanges, plaques were fixed to the sides of the locomotive, these stated 126 miles an hour, which has been the speed generally accepted ever since. Some writers have commented on the implausibility of the rapid changes in speed.