The engineering yield strength, the modulus of elasticity, the original diameter and final diameter of a wire are given. That wire is stretched and it diameter decreases. I am trying to find the engineering strain just before yield and the corresponding true strain. So I assume I will find that the engineering strain is equal to or very close to the true strain because their curves don't diverge, in my experience, until necking occurs but I have to show that is the case. I believe that the yield strength is at the yield stress so a good approximation would be the proportionality limit. My problem is that there are no specifics about the modulus elasticity. If it is young's modulus then I can find the lateral strain from hooke's law but then because I don't know the original or final lengths I don't know how to compare it to the true strain. Is there another law that I am forgetting about? Is hooke's law applicable for the longitudinal case?