AT&T MERLIN Attendant System Manager's Manual page 45

Changing the Current Settilngs
number of digits are in an extension (two to four). For example, if you indicate
that only 2-digit extension numbers ranging from 10 to 55 are available in your
system, once a caller enters two numbers, the MERLIN Attendant quickly
determines if the extension number is valid and immediately transfers the call
without waiting for further input from the caller.
NOTE:
Occasionally a MERLIN LEGEND system may have extension numbers
composed of various numbers of digits. For example, a system may include
extension numbers 29 (a two-digit extension) and 2489 (a four-digit
extension). In systems for which the number of digits is mixed, you must set
the "Extension Digits" Call Processing Option to 19. The "Lowest Extension"
and "Highest Extension" Call Processing Options cannot be used when
"Extension Digits" is set to 19.
Table 2-3 gives a description of the call processing options, the default setting
for each one, and the possible settings you can use. The last column can be
used to record the current setting. Refer to Planning Form H and the
programming instructions following the table to change any of the values
listed.
2-20 Changing Call Processing Options