A drilling process has an upper specification of $1\mathrm{.}751$ millimeters and a lower specification of $1\mathrm{.}649$ millimeters. A sample of parts had a mean of $1\mathrm{.}7$ millimeters with a standard deviaiton of $0\mathrm{.}027$ millimeters.

What is the process capability index for this system?

Note: Round your answer to $4$ decimal places.