Typesetting unit (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">typesetting unit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for pica that I've seen before include "size related to type" , "old type" , "Magpie's" , "Measure" , "Unit of type size" .)