FM's the State of Play with empasis on Climb performance.

[Ernst]

And more there were some error due the fact there is no guarantee that the pilot used the maximun aircraft performance only because he is human. Was the tests repeated extensively do determine an average that the pilot can climb the aircarft? Yes or no? Due to this the relative (difference in) climbs are in good agreement. Second the quantity represented is not rate of climb.

From the error theory the error should be the minimun grade/2, i.e, sigma = 2.5ftm/2 = 1.25m = 1m15s. Considering this error the relative climbing can be considered in good agreement.