Apple Numbers x-axis “Value Labels” can’t be set to “Date & Time” or “Duration”

numbers

I am graphing a two-column data set that looks like this:

1/1/1963    3,209,827,882
1/1/1964    3,281,201,306
1/1/1965    3,350,425,793

But when I try to set the Value Labels in either a Line Chart or a Scatter Plot to "Date & Time" or "Duration" I find that they are greyed out.

Why would this be? In what situations is it possible to use these two options?

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Best Answer

Make sure the source columns are formatted as the proper date/time format.