The Game of Bluesticks

Seemingly not having bought enough plants from the nursery yesterday I went back for more while E went off to see A in Worcester.  I came back with one of the flowering cherries we'd eye'd up yesterday.

The process of working out the best place to plant it to obscure the most neighbourhood while fitting in with the overall plan (plan?  There's a plan?) involved much walking around with one of the roofer's unused battens.

There is a complex reason why the batten is blue; but I've forgotten it.