How would one calculate the availability of nucleotides to an enzyme like a polymerase ?

I imagine an answer in units like nucleotides per second per enzyme, but I'm also imagining an answer that is not a simple rate of reaction. k_on calculations and k_off do not offer mechanistic explanation.

I'd like to know, specifically, if there is a theoretical approach to this question: how does a polymerase reject an incorrect nucleotide?