this is slightly orthogonal but i find manuals written by the original equipment manufacturer are better than 3rd parties (ford vs haynes for instance)
Just to point out the beauty of how a clearly defined black-and-white mathematical term (just use the dot product!) becomes malleable once it enters language as a metaphor. There's great humor in being "slightly orthogonal".
(Hopefully this doesn't come off the wrong way - just my mostly useless degree in linguistics acting up again.)
At which point is something slightly orthogonal - perhaps if it's between 1 degree and 45 degrees off topic, while if it is between 45 degrees and 90 degrees it is considered "fully orthogonal."
I found it varied wildly - the official manuals were incredibly detailed and covered everything - the Chilton guides would tell you how to avoid some weird $500 tool by using a crowbar and a dead chicken.