for this there is no need to go with categories or datetime of the x axis just change the data
in this format
: [, [x1, y1], [x2, y2], [x3, y3], [x4, y4], [x5, y5]]
ex:
data: [[1750,106], [1800,107], [1850,111], [1900,133], [1950,221], [1999,767], [2050,1766]]
update your js script please check http://jsfiddle.net/vKLPP/1/
hope it will be useful
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