Here is a picture of my current (lousy) attempt at uniform spacers
between flagstones to be set into mortar tomorrow:
http://www4.picturepush.com/photo/a/...mg/7478342.jpg

The board in that picture, placed with the tall side up (instead of flat
as it is in that picture), is still too thick.

Q: What do YOU use to space flagstone while you're cutting the last piece
and when you start mortaring them down?
http://www5.picturepush.com/photo/a/...mg/7478368.jpg

Note: It matters greatly even a little bit because the errors add up over
the 20 or so pieces and you're cutting the last (middle) piece to fit.
http://www4.picturepush.com/photo/a/...mg/7478407.jpg