How do you work out Young's Modulus?

[Gallows]

I am really finding it hard to work out Young's Modulus.

I have my stress / strain graph

I was told I should apply a gradient on the graph to work out youngs modulus

The strain is in (m) and the stress is in (nm-2)

How do I work out the youngs modulus, and what unit of measurement would youngs modulus be in?

 

[AJ Bentley]

Look in Wikipedia. It's a good explanation.