In the fifties and sixties Bomber Cammand runways had a line painted across the runway at 1500 ft. from the start point. On the Vickers Valiant you calculated the speed; dependent on weight, temperature, pressure altitude and headwind component; that which you had to pass over the line to confirm that all engines were providing the calculated thrust. You normally passed over it with an extra five knots or so and at that point the PNF would call "Up Five". Any "Down" call would require an abandoned takeoff. This was neccessary because in some scenarios the Stop Speed, where you could stop on the remaining length of runway in the event of an engine failure, was before the Safety Speed, where you could continue the takeoff.