What I do is place a 123 block on my plate.
I have a Rayco plate so it is easy to get that square.
When I put the star in I eyeball it square to the block.
Your dual calsphere needs to be pretty square to the machine also.
Next, I calibrate each tip individually, starting with #1.
It might take a few tries, but it'll work.
Here are a couple of pics of how I do it.
