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but from what I´ve seen, this targeted minimum upvote value changes too.
It said 0.14 yesterday, today it says 0.18.
this is the part I do not get.

That's the part that's faulty. Our actual minimum upvote target is $0.02; we recalibrate the minimum vote target (in rshares) once a week by comparing the estimated value of the minimum votes we're actually delivering to the target value.
When market conditions are more volatile, the accuracy of this estimation decreases.