For the past few weeks the Best Grandpa in the World has been building a railway track all round the inside of the tank. 00 gauge and 144 feet long. Please understand this is for James and Ben - not for BGitW himself. Ahem. The track runs on a 4" wide shelf right round the tank.
Here we see James (9) showing Ben (5) how things are done.
click to enlarge
Enough of such techno twaddle. Main thing is that two little boys think BGitW is wonderful.