A metal fabricator produces connecting rods with an outer diameter that has a $1+-0\mathrm{.}02$ inch specification. A machine operator takes several sample measurements over time and determines the sample mean outer diameter to be $1\mathrm{.}004$ inches with a standard deviation of $0\mathrm{.}003$ inch.

Calculate the process capability index for this example. $($Round your answer to $3$ decimal places.$)$

Process capability index