This excerpt taken from the PCG 10-K filed Feb 18, 2005.
4.3.1. Calculations of Annual Availability Performance Indices for Individual Voltage Classes
Separate annual Availability performance indices shall be calculated for each Voltage Class and PTO as described below utilizing the Availability Measures discussed in Section 4.2.
Annual Average Accumulated Forced Outage(IMS) Duration for those Transmission Line Circuits with Forced Outages(IMS) (Index 2):
Annual Proportion of Transmission Line Circuits with No Forced Outages(IMS) (Index 3):