The only way I could duplicate your result was if the 2900th X value was text, not a number. This causes the chart to treat all X values as non-numeric labels, giving the chart the appearance of a time series.

Like the proverbial bad apple, it only takes one non-numeric X value to screw up the whole set of X values.

The non-numeric X value might be a number formatted as text. Remove horizontal alignment from the data, and look for a number that is left-aligned, unlike all the well-behaved, right-aligned numbers.

There is a very restrictive limit in X-Y scatter plots. I’ve found that when the two series charted exceed 2899 data points, the chart turns into a time series plot of just the second (Y) data set. My data ranges from 0-10 in the X series, and 0-16 in the Y.

Obviously in such a chart there are many overlying data points, a situation not addressed in your comments. The chart remains usefull though, in highlighting relationships amongst extreme values in each series. Further, by modifying the point shape, colour, and border style (in my case, changing one feature each month in the daily data), much of the time series value of the chart is retained. This makes it almost a 3-D chart, very valuable analytically.

Excel 2003 (from which I just switched to Excel 2010) did not have this restriction.

Any insights or work-arounds would be appreciated.

Given that Excel 2003 can only utilize 1 GB of memory, and Excel 2007 can only utilize 2 GB of memory, but Excel 2010 can utilize (in theory) 8000 GB of memory in its 64-bit version . . . is it almost time for power users (or their employers) to invest in a new computer with a 64-bit OS and 6 GB or more of RAM for our bigger spreadsheets?

Dale

THANKS !!