How to use a graphic flight computer to find ground speed and true heading<br>Align the wind direction under the " true index " mark by rotating the azimuth plate. If the winds are from 330 ° at 20 knots, align 330 under the true index. Align the grid so the center grommet is over one of the heavy lines.
ground speed and true heading can are best found with a graphic flight computer
The context only states it is a way to do measure flight speed, not that is the best. There might be a better method. The system could likely not interpret the use of the word best as meaning the top method. 
( z0 find :ARG1 ( z1 and :op ( z2 speed :mod ( z3 ground ) ) :op ( z4 heading :ARG1-of ( z5 true ) ) ) :ARG1-of ( z6 have-degree :ARG2 ( z7 good :ARG1 z0 ) :ARG3 ( z8 most ) ) :ARG1-of ( z9 possible ) :instrument ( z10 computer :mod ( z11 fly ) :mod ( z12 graphic ) ) )
(z0 / find-01
    :ARG1 (z1 / and
              :op1 (z2 / speed
                       :mod (z3 / ground))
              :op2 (z4 / heading
                       :ARG1-of (z5 / true-01)))
    :ARG1-of (z6 / have-degree-91
                 :ARG2 (z7 / good-02
                           :ARG1 z0)
                 :ARG3 (z8 / most))
    :ARG1-of (z9 / possible-01)
    :instrument (z10 / computer
                     :mod (z11 / fly-01)
                     :mod (z12 / graphic)))
ground speed and true heading can are best found with a graphic flight computer
z2 :mod z3
z1 :op1 z2
z4 :ARG1-of z5
z1 :op2 z4
z6 :ARG2 z7
z6 :ARG3 z8
z7 :ARG1 z0
z0 :ARG1-of z6
z0 :ARG1-of z9
z0 :ARG1 z1
z10 :mod z11
z10 :mod z12
z0 :instrument z10