There have been a few questions as to why the HBA tiles are being installed in the order that they area. Direct from Chilbolton, here is the reason...
The connectors for each tile are on the south west edge. Because access is needed to make these connections, it is imperative that this side is kept free as the tile is being placed. In the example, the connector location for #64 is shown. If #64 was placed *before* #53, it would then actually be impossible to place #53, as there would be no access to its cable connections. This is why the tiles must be placed starting at the northeast and working south west in any given column.
Then there are the complications. Locations #6, #14, #21, #27, #31, #34 and #44 have problems with the cables (marked with crosses). Until these problems are fixed, we cannot place the tiles at these locations. This then effectively blocks that particular column. So, for example, we placed #12, #22 and #33, but because we cannot place #44, this column is then blocked from further placement.
Then, Tile #C is special. It has not been delivered to site yet. Until it has arrived, it presents another obstacle that we cannot pass.
Furthermore, the digger can only drive down certain columns due to the placement of survey pegs. The digger also has limited reach. Where it is shown at the moment, it can easily reach #69 and #70. And, because we do not want to turn the digger on the field (to preserve the surface), we can only go along the green lines.
And, once you've placed a tile, you can no longer drive passed it. So, if we place #70, we could no longer place #58.
So, following the initial placement from digger track A and B, we have moved the digger to track C, where there is a clear run of tiles that can be installed. While this is going on, repair work is being done on location #31, so after track C is complete we'll be able to reach #20, #31, etc. from the southeast edge.
Due to the various blockages, this is the most efficient way to proceed. Think of it like playing Tetris with an 18-tonne digger and 5m x 5m blocks!