Why is it the case that "in the technical sciences" propositional logic it is accepted that If P = FALSE then Q = TRUE = TRUE?

P = False Q = True

Every calculator I use states: If P then Q = True. This is commented on in the sources I can find: http://www.math.hawaii.edu/~ramsey/Logic/IfThen.html

Most of the question is in the title. I'm wondering not why this is the case, exactly, but why it is accepted that this is the case. What is the underlying decision that resulted in this being considered the norm?