So using 2015 there isn’t a R click Point At Center anymore, I was looking at this thread Restore Point at Center
but don’t know much about ruby or ad ons,
so how do I get it back?
If you download and install the su_examples_110.rbz file from the extension warehouse, you get Point at Centre in a context menu when you R-click on an arc or the edge of a circle.
AFAIK that’s the only place you’ll see it.
The function is built in to SU 2016 as Find Centre in the context menu.
Right on Dave, thanks for that, I think that’s the first extension I’ve ever downloaded 
Thanks to you too John!
How did I miss that? +1 Duh.
Another extension, Chris Fullmer’s tools, has an arc centerpoint function, which does the same thing as point at center
Yes and a huge improvement that was. But we shouldn’t rest on those laurels. It can still be quite a fiddle to get hold of the centrepoint. You have to hover over the circles’s edge until SU wakes up and realises what you want. I think this is related to another series of posts about how SU chooses magnetic points. There is no built-in override system. You might think you could force SU to only select end points, say, or circle centres, but you can’t. You get a similar problem in LO when trying to place dimensions. All could be improved I feel.
I think that is one that finds the centre from any two segments of an exploded arc. At least, there is one of his that does that.
Yes, you’re correct.