grammar - Article omission or not?

I'm not a native English speaker, so I'm often wrong when it comes to grammar. I usually go with my gut feeling.

I'm documenting some parts of an application and I was reminded that I often omit the the article in my sentences. So we started discussing individual cases but I was objecting to my very best knowledge why the should not be part of them but I'm not sure.

I would still like to write them correctly even though none of us are native speakers.

1. 
   

   The donut chart is used ...

   
   
   

   I wrote it without the article because in my understanding the refers to noun chart which in this case is well defined by the word donut so I would say it doesn't need an article. And it's about a donut chart that is the only one on the component I'm documenting.

   
   


2. 
   

   The chart slice sizes are ...

   
   

   I also omitted the article, but in the end I think my sentence was wrong, because article here refers to slice sizes and I should actually wrote it as Chart's slice sizes and of course without the article.

   
   


3. 
   

   top part with the date period selector

   
   

   This is the whole text of some bullet point. I omitted the article because it refers to a specific selector. A date period selector specifically.

   
   

Etc... As said, this is all very fuzzy to me.

Answer

Unless you are using "headlinese" for a specific purpose (as in a PowerPoint presentation, for example), then you would include the article; i.e.,

"The donut chart is used" to show the relationships, etc.

"The chart-slice sizes are" indicative of the relative importance, etc.

"The top part with the date-period selector" enables you to, etc.