Normalisation of a correlation function

Hi everyone

This might be a bit of a simple question, but I have spent a long time on this one and still cant work out the answer so I would really appreciate a bit of help from you guys.

I have been working with a theory that requires the correlation of two signals (decaying pulses). Initially I used the Pearson correlation function which wasnt too great at doing it but gave a reasonable idea of the situation so instead I started using a difference function, simply the sum difference, but I wish to change this to make this normalised. Does anyone have any idea how to do this?

As a side note, are there any other correlation functions which would suit this well?

Many thanks for all your help