CF crowd (apparently only Madman + BlueSky + Mike in NRH):

Please answer the following questions:

1) How is an airplane's speed measured?

a. Groundspeed
b. Airspeed
c. Other (specify)

2) What measurement devices are used to determine an airplane's speed? (Hint: --> click here <--.)
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4x4 in uppercase is $X$!!!
1997 R50: VG33E/RE4R01A/TX10/3.7/R200A/ARB/4.636/H233B/ARB/4.636/321150R15