PULGAR

n. thumb, innermost finger of the hand which moves in the opposite direction of the other fingers

Thumb. Symbol (right hand)-Upper case 'P'

= thumb.
Ex: Then he picked up about 2 cm. of type from the right-hand end of the uppermost line (i.e. the last word or two of the last line) with the thumb and forefinger of his right hand, read it, and dropped the pieces of type one by one into their proper boxes.
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* huella dejada por el pulgar = thumb-mark.