While Nicholson's Mechanic's Companion is busy having itself imaged, I've been doing some research to prep the introduction. Before there was the Mechanic's Companion, the book was published in 1812 under the title Mechanical Exercises. Although I haven't pinned down a reference yet, I can only assume that Mr. Nicholson realized that the title was a bit too close to Moxon's Mechanick Exercises and so saw fit to perform a bit of editorial initiative.
Courtesy of Google Books, I dug up a book review from The Literary Panorama of 1812, pages 50-51. For those who don't want to read the entire book, I've added a pdf of the relevant pages Download Nicholson 50-51.
Everyone is fond, myself included, of positing the meanings of past events. Why did an author chose to write a particular book, for whom was it intended and how was it meant to be used? Perhaps through years of researching engineering and medical stuff in libraries, I've had it instilled in me that unless you can find the seminal reference, it's all conjecture. On rare occasions we find a first person account by an author or publisher. Lacking that, a book review current to the time period does provide insight into what the book meant to the inhabitant of that particular cultural, industrial or geopolitical 'scape. True, it's the opinion of that reviewer, but I think it's safe to say that the reviewer of 1812 had a better sense of what was than do we in the here and now. Even reading between the lines provides a tonne of insight.