There seems to be something not quite right with the charting overlay process. The attached chart of FTSE100 with the All Share overlain doesn't line up consistently. Given that the FTSE100 is a major part of the All Share the daily moves should coincide should they not?

Eoin Treacy's view

Thank you for this chart but an overlay will only ever give us a rough approximation of how two instruments are performing.

If we plot the ratio we can see that the FTSE-100 has underperformed the FTSE-All share by a considerable margin over the last few years and this helps to explain the divergence in the overlay.