Essential elements of the abstract are:

    * Background: A simple opening sentence or two placing the work in context.
    * Aims: One or two sentences giving the purpose of the work.
    * Method(s): One or two sentences explaining what was done. 
    (Described at length only if it is unusual)
    * Results: One or two sentences indicating the main findings. (Absolutely 
    essential)
    * Conclusions: One sentence giving the most important consequence of 
    the work. (Telling what the results mean).

Questions an Abstract Answers

* Why did you do this study or project?
* What did you do, and how?
* What did you find?
* What do your findings mean?

If the work is about a new method or apparatus the last two questions
might be changed to
* What are the advantages (of the method or apparatus)?
* How well does it work?

An abstract should include the few things you would like your reader to
remember long after the details of your thesis may be forgotten.