0.25 → 0.35 → 0.42 → 0.197 → 0.203 → 0.19999.
But he did rename the file.
At 7:55 AM, he emailed Helena the results. He attached a clean sheet with one button: “Calculate Vol.” He didn’t tell her about the PDF. He didn’t mention the cold coffee or the 11:47 PM panic. How To Code the Newton Raphson Method in Excel VBA.pdf
“If you cannot calculate the analytic derivative, use the Secant approximation: f’(x) ≈ (f(x + δ) − f(x)) / δ.” How To Code the Newton Raphson Method in Excel VBA.pdf