It should be known, that for modern mechs, Shimano actually give a distance.
In lowest gear (big back, small front) tooth to tooth should be 5-6mm gap.
Worth a quick read as other than minor wording and picture changes, they instructions have not changed much over the many years, even the SIS indexing bit.
Modern shadows http://bike.shimano.com/media/techdocs/ ... 746412.pdf