AE Director System from the 1926 edition of "Machine Switching, Volume 3" by International Textbook Company of Scranton, PA. Copy provided by Alan David.

Electrical Communication Systems Engineering - Chapter 8 - Foreign Central Offices From a US Army Technical Manual Submitted by Chris Mattingly.

Editor's Note by Chris Mattingly.

From the September 2000 Switcher's Quarterly: The 6A Key System - Part III by Joel Eves. Part of a series detailing the KTUs found in the 6A key system.

From the October 1998 Switcher's Quarterly: Direct Inward Dialing by Bruce Crawford. The independents provided it for years. See why Bell took so long to catch up.

From the April 2003 Switcher's Quarterly: The Day I Turned Off the Main Breaker by Keith Hlavacs. Find out why anyone would want to turn off the main breaker in a CO and still expect to keep their job.