Since a few chain adjustments I noticed that the left hand side of the handlebars was starting to feel a bit further forward than the right when riding in a straight line. Setting up a make shift wheel alignment jig using a length of aluminum angle & a straight piece of timber running the length of the bike & the width of the back wheel showed the wheels were out of line.
I have found that trying to read the markings on the swing arm from the square blocks that the axle runs through is a bit vague. A dig around in the jar full of junk that will probably come in handy one day I found some bits of metal from an aluminum picture frame, cut and bent into shape to form a more easy to read marker.



Fixed on the bike goes something like this...



Hopefully this should take a little bit of guess work out of wheel adjustments now.