The German electric guitar group called Gitec https://gitec-forum.de/wp/en/ has translated the rest of Chapter 4 of "Physics of the Electric Guitar" (which they refer to "PotEG" for short) into English. PotEG was written by Manfred Zollner, and at over a thousands pages, it's probably the most in-depth book of this type. Here is a link to the index https://gitec-forum.de/wp/en/gitec-...ectric-guitar-with-links-to-the-chapters-pdf/ , all of the translated portions are distinguishable from the green hyperlinks. Sections which have not been translated have no hyperlink yet. So often when talking about the physics of electric guitar, there is talk about what is theoretically true, but in addition to explanation of the physics concepts, the book includes lots of actual test data, so the extent to which things are true, and whether it is relevant to the final tone, can be deduced from this hard data. Chapter four deals with magnetic fields, in nearly every respect that they concern guitar pickups, from magnetic alloys to how the permeable masses interact with each other in the final magnetic circuit. Section 4.11 is especially novel, it talks about the effect of magnetic string pull upon the strings, which touches on the underlying differences that are caused by magnetic strength and pickup height settings. The way the pickup pulls upon the string subtly effects the timbre of the instrument. Chapter five, also in the linked index, discusses particular models of pickups, and is also mostly, but not yet entirely translated. While chapter four is rather dense with concepts concerning physics, chapter five is rather accessible, and it gets down top business. A large amount of this information is new to the English language, either for how it relates physics to the specific application of guitar pickups, or the application specific data which it presents. If you just browse through the sections, you're sure to find various interesting insights about magnets, magnetism and pickups.