That is not what I said. I said the the attraction of the iron in the nose mounted engine - if not magnetized, is insignificant compared to the effect of magnetized metal in the fuselage.
I didn't say that.
You remind me of the story of two brothers.Bill and Bob. Bill was a scoundrel. He had been in just about any kind of trouble you could imagine, leaving bedlam in his wake - ex wives and illigitamate offspring and a criminal record as long as your arm. He died. His brother Bob went to the pastor who was in charge of the funeral service and offered him $1000 extra if he told everyone his brother was a saint. Small-town pastors are not terribly well paid - he figured he could really use the money. At the funeral service, the pastor said "As you all know, Bill was a scoundrel, a theif, and a womanizer,There really isn't a whole lot of good I can say about him, but compared to his brother Bob, Bill was a saint!"
We don't know what kind of Semi he's talking about installing it in. Aluminum cab, steel cab, or mostly fiberglass. A set of non-sheilded stereo speakers in the dash of an aluminm cabbed Pete are going to cause more havoc than a 400 Hp Paccar up front, compass-wise
Emeraude and Jodel too. The compass can be compensated to within a degree or two with no problem Starter current can spin the compass on the jodel.
Can't compensate for a magnetized loop. Particularly if the compass is mounted to one side or other of the panel.