If you replace the first row of data as in the example 'sample21' from the module:

    ['1st','2nd','3rd','4th','5th','6th','7th', '8th', '9th', '10th'],
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you will see that it's nothing wrong with the graph, your expectation is wrong, the first value is 0, the second is 1 and so on. This is not a graph in the mathematical sense where you plot a function like y=f(x).