You raise an interesting point. What are the quintessentials of the Ingenieur line. My initial response was "definitely antimagnetic", probably followed by Pellaton. However, Michael's response made me think again. What separates an IWC Ingenieur from other watches?
This is what Larry Seiden et al. wrote in their article about the IWC Ingenieur: "The Ingenieur's genesis dates from 1944 when IWC hired a new technical director, Albert Pellaton. He was responsible for the creation of IWC's first automatic watch, the calibre 81 (subseconds at 6) and the calibre 85 (central seconds, flat overcoil) in 1950. The next generation, the calibre 852 (central seconds, Breguet overcoil) was the first automatic movement encased under a soft-iron core with the Ingenieur name. The Ingenieur was viewed by IWC as the automatic and civilian version of the famous Mark XI, a hand-wound antimagnetic classic whose fame and following grew as a modern pilot's watch. The Ingenieur is not a spectacular or sexy watch nor was its introduction in 1955 widely anticipated. Like the Mark XI, the Ingenieur is about function and the name translates literally to "engineer." However, because it was produced for the civilian market, the Ingenieur was offered in a variety of relatively elegant dial styles, as well as in 18kt and mixed (steel and gold) cases. Today the timeless design of the watch puts it in the "classic" category and is testimony that its appeal has outlasted its long reign as the flagship of the IWC line".
And: "The famous Ingenieur logo of the arrow passing through the name is reminiscent of the Swiss thunderbolt icon that warns of an electrical current's presence. In this case, the thunderbolt was chosen to represent the Ingenieur's anti-magnetic properties, i.e. the ability of its special soft iron shield construction to protect the watch against magnetic fields. The logo makes the watch easy to identify from other IWC automatics of the period and gives the watch its joie de vivre".
So the logo seems to represent antimagnetism as a discriminating feature. But then again, pilot watches were antimagnetic too.
Might it be better to define the watch as "A watch made by engineers for engineers?". This seems to be confirmed by Seiden et al: "The Ingenieur's desirability among today's collectors is difficult to explain, but its status as one of the earliest "tool" watches, combined with its rarity, technically advanced movement, and timeless design, make the Ingenieur something truly unique. The Ingenieur is also quite large for a vintage watch (36.5-37.2mm for pre-Jumbo Ingenieurs) and its heft (due in part to the soft iron casing) makes it quite a presence on the wrist"
All in all my personal conclusion is that antimagnetism is NOT a discriminating feature. The Ingenieur is an TOOL watch with advanced technical features, that may but does not need to include Antimagneticism.
Note: They refer to MF's article "THe IWC ingenieur: the incomplete history" but I could not quickly find that one unfortunately. Perhaps MF could share the link?
Thanks for asking the question!
Best wishes, Peter