10^–15 is not a negative number, just a small one. https://www.wolframalpha.com/input?i=10%5E-15+

And it is less than one?

	▲	JadeNB 2 hours ago \| parent [-]
		I think my favorite part of that comment is "documenting" that 10^(-15) is not negative by appealing to Wolfram Alpha.