We've positioned 3 blow hoe tubes in the top which should provide us with plenty of information about the atmosphere in various parts of the chamber while firing as well as giving us a useful stoking guide.
We managed to build a little more than this image shows, putting in another blow hole tube at the top, and a cone viewing hole in the side arch wall.
So, lots more cutting to do this week to get all those tail bricks to fit good and strong and then filling any external gaps with slithers of brick and ramming with dry fireclay. Then, continue to build up the chimney and start the secondary arch. :-)