You could use the free transform (cmd-T) and then position it exactly, using the center dot
setting the center position of x and y to 1800 pixels would put it at the exact center of a 12 in page at 300 dpi.
Once I finally figured out what that little grid of dots was, I started to use it a lot more
It' great if you want to put something in a specific spot (upper left/center/etc.)