A key joint in a precision machining process has a lower specification limit of a width of $0\mathrm{.}99mm$ and an upper specification limit of $1\mathrm{.}01mm.$ The standard deviation is $0\mathrm{.}005mm$ and the mean is $1mm.$ What is the process capability index for the precision machining process?

Multiple Choice

$0\mathrm{.}01$

$0\mathrm{.}99$

$0\mathrm{.}67$

$0\mathrm{.}33$