Headings

Hi,

I'd like to create a table of contents for my PhD thesis. I've assigned the style Heading 1 to my Headings and created a table of contents. This has worked fine, however, I'd like to include a numbering system in my headings. By this I mean I would like to have for instance:

1 Introduction
1.1 An introduction to the telomere
1.1.1 The structure of the telomere
1.1.2 The function......
2 Materials and Methods
2.1 Chapter 1
2.1.1 DNA extraction

and so on.

I can see that if I click the arrow next to Heading 1, then go to modify, then go to format, and select numbering and go to define number format - I can change the numbering format to 1.1, but then it thinks I want to have 1.1, 2.1, 3.1 etc instead of 1.1, 1.2 etc

Could you explain how I can set this up?

Many thanks,

Kara