“when doing something” or “when do something” or "when some is done"

Question

I have some troubles in determining the titles of my dissertation. In a chapter, I have several subsections, each section considers different circumstances, should I set the titles of these sections to be:

• When add link 1
• When add link 2
• when improve factor 2

or

• When adding link 1
• When adding link 2
• when improving factor 2

or

• When link 1 is added
• When link 2 is added
• when factor 2 is improved

Which approach above is preferred if I want my language to be concise and formal. Are they all acceptable in oral communication?

I think the expression "when add link 1" may not be proper or grammatically correct, what about the other twos? Are there any more recommended ways to convey the same idea?

Answer 1

The first three are simply incorrect grammatically

The second three and the third three are grammatically correct.

However, as a matter of style, the second three create a different expectation of what is being introduced than do the third three. "When adding X" uses a present participle and so tends to create an expectation that what will follow relates to the process of doing the addition. "When X is added" uses a past participle and so tends to create an expectation that what will follow relates to the results of the addition.