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Perception. 1991;20(3):415-8.

Thumb's rule tested: visual angle of thumb's width is about 2 deg.

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Department of Psychology, University of Otago, Dunedin, New Zealand.


Measures of the size of various hand parts and their viewing distance when held at arm's length were made on one hundred and eighteen undergraduate students. A simple rule of thumb can be confirmed: Visual angle of the width of the thumb held at arm's length is about 2 deg. The thumbnail subtends about 1.5 deg and the index fingernail about 1 deg in width, when both are held at arm's length. These figures are good approximations for males and females, although a significant, direct, linear relationship exists between hand-part size and the visual angle of the part at arm's length.

[Indexed for MEDLINE]

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