Where does Frequency analysis place the accelerometer? What is the pink dot on my model?

Hi everyone:

I'm trying to figure out the FIRST MODE of my structure (a Hexapid telescope) with frequency simulation. I have a question...where does solidworks place the accelerometer to measure the frequency of my structure? If you look at the PINK cube on top of my structure...what the heck is that? THANK ALOT!!!

SolidworksSimulation