How to locate a line parallel to adjacent building for a new building
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[*]-------------------------[-]---------------------[*] &lt;-- stake with nail   
 ^-- stake with nail at      ^-- stake at roughly           set under extended
     arbitrary distance          the same distance,         carpenter's line
     from bldg                   with mark at exact
                                 distance

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Set a reference line as shown, then just take measurements from that as needed.