You may be a good writer, but when it comes to writing technical manuals, much of what you’ve learned needs to be rethought. Technical manuals have their own sets of rules. These rules are well-known, and yet, too often I see manuals that ignore them. The most important thing to remember about manuals is that 99% of us don’t bother to open them until we have to. It is from this behavior that we get the acronym RTFM (Read the *bleep*ing manual). When people do turn to their manuals, they want all the information they need right there. For this reason there is no such thing as repetition in a technical manual. Treat every section as a complete entity. It doesn’t really matter if you’ve already explained something in Chapter 2, the reader isn’t looking for a narrative plot line. Like Sargent Joe Friday on Dragnet, they want “just the facts.”
Sometimes I am also called upon to illustrate manuals. The rules for this are the same as the rules for the text. There is no sin in repetition, If instructions in section 4 require several of the same images as section 2, there is no shame in reusing the images.
And by the way, here’s a tip for creating technical illustrations from photos. If you have to create several drawings of a piece of equipment, and you are working from photographs, put the camera on a tripod and lock it down. That way, the elements that don’t change from photo to photo only need to be drawn once.
Here is a link to a manual that I both wrote and illustrated: IW manual.