The right-handed sense of a helix traces out a clockwise rotation moving away from the observer; the left-handed sense of a helix traces out a counterclockwise rotation moving away from the observer, e.g. the ...TG + TG + TG + … helix of isotactic poly(propylene) is left-handed.
Source:
Purple Book, 1st ed., p. 43 (http://old.iupac.org/publications/books/author/metanomski.html)