Formatting grouped horizontal axis of Pivot Chart

Hi, I've got time-based data and I'm using a PivotTable to smooth data collected daily by grouping by in 7 day intervals and taking an average. I've plotted the smoothed data, but the axis shows each of the 7-day periods instead of the year as I would like (see "Problem Outline" attachment). I have tried to apply custom number formatting, but this appears to be ineffective (see "Ineffective Number Formatting" attachment). I've attached the actual spreadsheet in case it's of any help. I'm using Excel 2010.

Thanks.

Thanks Andy, but adding Year to the grouping means that you cannot group days in lots of 7 (see attachment), and so the data is no longer smoothed. I suppose this would make sense because a new year could fall midway through a 7-day interval.

But after more than 2 decades of development on Office to date and my wallet £200 lighter from its purchase, I'd have hoped that a simple axis formatting isn't too much to ask from Microsoft. Surely there must be some way to achieve my desired result?

Thanks again.

Thanks Andy - I thought of a possible solution by adding an extra column containing the year of the date in the dates column. This has allowed me to group by year then by 7-day interval as you had previously suggested. However, now, although the year displays as desired on the chart's horizontal axis, how can I remove the labelling of the 7-day interval subgroup (see "Subgroup-Labels Problem" attachment)?

The updated spreadsheet is also attached for reference. Thanks again.

Thanks for your help Andy. The chart is looking good, however, how can I move the horizontal axis labels closer to the axis (see attachment)? I realise it's because it's part of multi-level category labels, but turning that option off removes the top level category labels (Years) which is what I need to keep instead of the lower level (Weeks displayed as " ").

Thanks for your help.

Thanks Andy - what do you mean by "change the category axis range"? How do I do this? Thanks.