How do I implement a spatial dirative in simulink?

I have two signals, lets call them H and M. Now in simulink I would like to implement a derivative of dM/dH and spit out the answer. How would I do that?

Note: Can I do this without a zero order hold? (I've implemented a zero order hold and manually subtracted the changes to make (M(t)-M(t-1))/(H(t)-H(t-1)) but it's numerically unstable at small values.