line chart-format x axis for dates

[Scatter]

For a set of time series graphs as a line charts, I cannot repeat the feat of getting Excel to recognize the x data as a date in the Format Axis>Axis Options window and present interval choices as dates in the top portion of that screen. I blundered thru it once, but don't know how.?!?! A screen shot of the one successful example is attached. For all my different spread sheets, the data for the horizontal axis is formatted as date, plus set to date in the Number tab of the Format Axis screen.

I'm sure I'm missing something simple. Please enlighten the dim witted!
How can I consistently get the date style interval options?

[Andy Pope]

You will only get the option if all the data used for the axis is actually a date. If any of the cells is text or the date is not a true date then it will simply revert to categories.