This is supposed to be a general guide.

• focus on the math, science and engineering that is common in all cases
• avoid diving into the specific ways each individual tool handles things
• make as few assumptions as possible and clearly document them

Focusing on the general topic will increase value in the following ways:

• open source developers tend to start from scratch in at least one area; this will help them solve their unique problems
• open source users are often left to puzzle through incomplete documentation; this will help them fill in the holes
• everyone who uses 3D printing will benefit from a common core; this will help them leverage 3D printing's strengths while avoiding its weaknesses

Explain things visually

• a proper illustration needs little (or no) explanation
• pictures avoid using different words for the same thing
• diagrams usually don't require any translation
• it's easier to compare what you see on the screen to what you hold in your hand
• pictures can be shared and groked more easily