Power Trendline Equation used in a cell

Hi Chaps,

I have some graphs which use power trendlines, these change as I add more and more test data. I've looked just about everywhere and nothing seems to come close. LINEST is for straight line graphs (or I'm doing it wrong) and doesn't seem to give me what I need. I've attached the sheet I'm working on and hopefully it'll open on the page and you'll see where I'm trying to use it. On tab "Tare Full Service Plot" if I can link cells U3 and U4 to the graph equation it will solve all my problems.

Any Ideas?

Thanks in advance

Ginge