It might be useful if you were going to do some mods or otherwise work on the specific Teles he goes into detail on. Otherwise, perhaps not really essential. Here is the relevant section of the table of contents. Plus the full table of contents. I would have creased the page down to make it flat for the pic, but who knew the book was worth so much. I saw it for around $225 new on one internet book site, and even more for a used copy elsewhere. Cheapest on eflay was $60 in beat up condition. Also have the other books pictured. The Duchossoir One has some useful info and details, depending on what you are looking for. The one by Bacon seems the least technical. If you have a need for any specific section of the Balmer book, I could probably provide some visual assistance re a particular section.