Dome Top Dead Center

With my new dome the first thing to do was find top dead center of the dome so I could use this as reference when I start drawing all over it. To do this I placed the Dome upside down on a bucket and dropped a marble into it, where it stopped was top dead center, this is the easiest way in my understanding to find TDC.

Then I have started with the long process of sanding the outer dome initially using 150 grit sand paper and will slowly progress to 600.