A friend recently obtained a Lanagan & Hoke, Inc. Growler that appears to test armatures and work. It has a High/Off/Low Power Switch and a Test Light Switch, along with the Light and three probes that stand stored in the back. One probe has two contacts on it.
Would anyone know how to operate this device or have a book that explains the operation?
Google "Armature tester" and you'll find some info.