Spotless Dominoes

No 2 son doing his stuff helping to set up the Domino project which is part of the local festival.  They are in a line winding their way throughout the shopping centre.  This evening the first one will be pushed over and if all goes well it will take 25 minutes from start to finish for them all to topple.  He is a volunteer in one of the 14 teams who will have erected 6500 blocks.  They are about 1 yard apart and are a type of concrete.  He started at 10.30 this morning and will finish around 7pm tonight as they have to clear them all away afterwards.  I originally thought I would volunteer but decided I am not physically up to it at the moment!!!