question about the length of the brass

I was just wondering, what do you do with the length that we measured for the cylinder. We found a relationship with the strain and displacement to find the strain values past 30 so we don't need to use it there. Where else would you need to use the length?

So, because we did have the measured displacement data from the computer, the final length measurement is largely superfluous and just more of a reference for you to have. You don't have to use it if you don't want to; I would say if you did use it, it could just be a sanity check for the strain vs displacement relationship you mentioned, but you certainly don't have to.