Fujita-Pearson Scale of Tornado Intensity 
    F0 - F1 F2 - F3 F4 - F5
    Weak Tornado Strong Tornado Violent Tornado
    F0 40-72 mph Gale tornado -- Light damage. Some damage to chimneys; break branches off trees; push over shallow-rooted trees; damage sign boards.
    F1 73-112 mph Moderate tornado -- Moderate damage. The lower limit is the beginning of hurricane wind speed; peel surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads.
    F2 113-157 mph Significant tornado -- Considerable damage.  Roofs torn off frame houses; mobile homes demolished; pushed over; large trees snapped or uprooted; light-object missiles generated.
    F3 158-206 mph Severe tornado --  Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.
    F4 207-260 mph Devastating tornado -- Devastating damage. Well-constructed houses leveled; structures with weak foundations blown off some distance; cars thrown and large missiles generated.
    F5 261-318 mph Incredible tornado -- Incredible damage. Strong frame houses lifted off foundations and carried considerable distance to disintegrate; automobile sized missiles fly through the air in excess of 100 meters(109 yards); trees debarked; incredible phenomena will occur.
    F6
    -
    F12    		 319 mph -
    MACH 1
     the speed
    of sound    		 The maximum wind speeds of tornadoes are not expected to reach the F6 wind speeds.
    Whose scale is it?
    The Fujita-Pearson Scale or The Fujita Scale?
    The scale was original created in 1971 by Dr. Fujita as a way of determining the strength of tornadoes from the damage that they caused.  Like many of the contributions of Dr. Fujita, it was not widely accepted when first published.

    Dr. Fujita and Dr. Pearson two years later published a paper that added in factors related to the width and length of the tornado path, and called the scale the Fujita-Pearson Scale.  It was this work that caused the scale to gain acceptance.

    The Storm Prediction Center now uses the greatly improved Fujita Scale to determine tornado strength from the damage that the tornado causes after the tornado.

    Yet when a spotter or anyone else from the field makes a judgment about the size of a tornado without damage data, but on the width and length of the tornado path, they are making that judgment based on the size of the tornado on the ground, which is the Pearson method.