I went for about 2 years with this problem and even Microsoft would not
help. They changed something between 97 and 200x and said that they
left that function out.

I have found a work around here on this tip forum.

2 different charts will work but both involve adding the date in one
column and time in the other column together in an inserted column.

Say your date is in column A and your time is in column B. Insert a
column C and in this column sum A and B. Make sure the format is
correct in all of the columns and no text characters exist in column A
or B. The reason I say this is that I found out that there were space
chacters in my time data that I never had a problem with until I
started this data sum. 97 just graphed the two and knew what it meant.
So much for upgrades huh.

Now build a line chart with column C being your X category axis and the
rest of your data being on the Y axis. It will look strange at first
but don't panic. Either while building the chart or after, go to the
"Axis" tab of "Chart Options" and change the radio buttton under
"Cateogory (X) Axis" from Automatic to Category. Now it should look
better.

You can also you a XY scatter chart but it does some funky stuff with
your timeline. The one above is a lot eaiser to work with.

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