Created attachment 81418 [details]
sheet containing chart behaving as stated

Chart of data against date. (Example attached)
The need for non-integer is to make an axis that over a period of a few years, approximates to month starts
So 60.875 days starting at 1/1/11 will after 4 year give 1/1/15  (365.25 days per year)
(see example)

If scale of the test chart shown is set to 
   minimum   1/1/11
   maximum  Auto
   Major interval   60.875
          the x axis will correctly show dates 1/1/11 to 1/1/15

Then click on the x axis and via right click click on 'format axis'

On the Scale tab the major interval will show as 60.
Make no change but click on OK
The x-axis labels will change to a major interval of 60.