The quality assurance manager is assessing the capability of a process that puts pressurized grease in an aerosol can. The design specifications call for an average of 60 pounds per square inch of pressure in each can, with an upper specification limit of 65 psi and a lower specification limit of 55 psi. A sample is taken from production and it is found that the cans average 61 psi, with a standard deviation of 2 psi. Also, the process will stop if the process starts making cans that are more than three standard deviations above or below the average. What is the capability index of this production process?