Dates of signs and decanates

Hi,

I am making a script that needs to be able to check which sign a date is in, and even which decanate. My question is, do these dates change ever, at all? I mean is there ever a chance that they'd change even minutely from year to year? Or are they fixed?

If they are not fixed, how can they be calculated?

Same goes for the decanates.

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Thanks, I think I can work from there. I'll be programming in PHP, but I think it'd just work if I execute swetest and parse the output.

Anyway, as for the decanates: [0, 10] degrees of any sign would be the first decanate, (10, 20] the second, and (20, 30] the third?

Thanks.

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