Thanks for the link, but I do already have that. It's just that I didn't bother with it as it's quarterly data.
I could just do a bit of averaging (or something), but I had the vague nagging doubt that quarterly data isn't just monthly data added up for three months. I can't back this up with any maths you understand, but it did occur to me that just 'playing jazz' with the quarterly data might produce misleading results...
Perhaps someone else can make soothing noises about doing this... or just tell me the best way to produce good monthly figures from quarterly data, and, hence, a new chart!
Save a copy before you start.
1. Copy and paste the data from the linked spreadsheet in to your spreadsheet. Date (quarters) and Price
2. Press CTRL and H
3. Type ‘Q1 ‘ in the first box and ‘01/01/’ into the second box. Then click ‘Replace All’ (note, there is a space after Q1)
4. Do the same for the other quarters
5. Right click the chart and select ‘Chart Type’. Change to ‘XY (scatter)’ if it isn’t already selected
6. Now add the new data line
7. Right click the new data line and select ‘Format Data Series’. On the patterns tab, you can match the line type to the other nationwide line so they both look the same.
The Nationwide data will look like it is one continuous line switching from quarters to months (but it will be shown twice on your key)
Come back to me if this wasn’t clear