The [index] section of a configuration file contains options used to determine the start and end years of climate indices (such as El Niño 3.4):

## options related to producing nino index.

# start and end years for El Nino 3.4 analysis.  Out-of-bounds values will lead
# to an error.
startYear = 1
endYear = 20

Start and End Year

A custom config file should specify a start and end year for time axis. Out of range year will produce an error.