Slope of The Non Linear Stress Strain Curve at Proof Stress

Dear All

Hi..

Can Any body tell Me The calculation of the E_t Tangent And E_s Secant Modules VAlues of the Stress Strain curve?...

i had go through some of graphs but i dont get it?..it will be help ful to understanfd the E_t And E_s?..

i had values of Stress and Strain and also a Stress strain curve available..

Plz do need ful..