[] This sets up the length of the major ticks. The actual length is the product of the default length and a scaling factor as for character height.
[] def (PLFLT, input):[]The default length of a major tick in millimeters, should be set to zero if the default length is to remain unchanged.
[] scale (PLFLT, input):[]Scale factor to be applied to default to get actual tick length.
¸plsmin, plsori, plsmaj, API
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