Arbitrary Horizontal Gridlines - for X,Y Scatter

Excel experts,
I am at a loss of how to go about this using Excel 2007/10. I was very much hoping to refer to Jon Peltier's treasure trove on charting, but alas I get a 404 Error on the exact link I was hoping to access, particularly:http://peltiertech.com/Excel/Charts/...Gridlines.html

I have multiple data sets with irregular timestamps, so I am committed to using an X,Y scatter plot. I would really like to be able to set up the Horizontal Axis to create vertical gridlines at the start of each quarter of the year i.e. Jan, April, July, October. I know I could try to use spacing of 91 days which would be about right but it wouldn't be exact.

I am aware that this is most likely not very straightforward and may involve using some dummy series to do it.

If anyone can please assist - or if you happen to have an example spreadsheet that would be much appreciated!

Hi there,

Thanks Jon for your prompt response!

Unfortunately I have to use an XY Scatter plot as the data I am working with has irregular timestamps between the series. That is to say (as attached) the multiple series don't all share the same timestamps.

I am trying to avoid wimping out by just using vertical lines here as I would love to keep the chart dynamic without manual adjustments. I have attached a sample of the data I am working with. Essentially it would be awesome if I could have vertical gridlines de-marking either the start of each month or start of the quarter. I was going to see what the approach was for quarters then later apply it to months as well.

Thanks for all your help

Thanks Andy and Jon for the assistance. Will have to change the thread to solved now!

Pretty impressed that both gurus helped out. Cheers!