For those of you who have printed off the pattern and found it to be not exactly 9" here is a solution kindly discovered and shared by Pat Harvey - thanks Pat.
When you select “print” in Adobe Reader 9, a print “dialogue box” opens.
One of the options is “page scaling” – half way down the box on the left.
If this is set to anything other than “none” then Adobe will adjust the size of the diagram to fit neatly on the page. The exact size will depend on the maximum usable area on the page – which will depend on the printer and some of its settings (and these will depend on the printer make and model).
So, select “page scaling” = NONE – and the print size should be OK. The alternative “fit to printable area” appears to be the default.