the gizmo is quick- way quicker than measuring- i used to measure before i was let into the gizmo secret.
besides as said above, the gizmo doesnt lie.
one word of caution with a tillering stick, i strongly advocate against using them- having a wood bow under tension( the longer the draw length the worse it is) while you study it- will lead to increased set- and in a few cases i have seen hickory bows blow up- while people sit there and take their time.
i won't use them anymore - just an unnecessary risk.
each to their own i guess- many ways to skin a cat!