It strongly depends on your notion of "ok" ;-)

The last line, in the very least, gives me headaches. Do you really want to return 7 references from a subroutine and remember what they are and in which order?

I'd suggest the usage of a hash ref instead: 

return {
    metadata => $hashref,
    above    => {
        x => ...,
        y => ...,
    },
    below    => {
        x => ...,
        y => ...,
    },
    on       => {
        ...
    },
};

[download]

As for the mathematics involved I didn't see a flaw. But you should test it nevertheless, with small sets of selected data.

In reply to Re: Positioning in relation to trend line by moritz
in thread Positioning in relation to trend line by Win

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