Need some help with sensitivity/elasticity analysis

[Sportfreunde]

I'm trying to figure out how to do an elasticity and sensitivity analysis by changing some values on a life table (lx and mx). I'm using Populous software to do this so it automatically gives me the new leslie matrix and new lambda values when I change a certain lx or mx value. My question is say that I'm changing the value for m6 from 6 to 1. The change in lambda is from 1 to 0.85. What value on the Leslie matrix do I look for to change to plug in to the equation? Do I only look at what the change in the f1 value is (it's 0 in this case) or do I look at what the change is in say the f6 or p6 value or whichever one which is from 1.80 to 0.44? Would my final equation for the sensitivity analysis be this?:

(1 – 0.85) / (1.8 – 0.44) = sensitivity

Or would my equation be:

(1 - 0.85) / ( 0...the change in the f1 value) = sensitivity?

Also, what do negative numbers mean in terms of elasticity and sensitivity? I've read that it's okay to get a negative number but don't really understand why.