Best way to centerspot my mirror

Thanks guys who posted ideas for centerspotting my primary. After plenty of alcohol and reinforcing tabs, I finally got it right. I measured my mirror precisly using a ruler accurate to 1/100 of an inch, then I marked a string with the precise diameter.

I took a piece of poster board and put a tiny hole in it. Then I treaded the string through the tiny hole and taped it on one side, with the first diameter mark right in the hole. Then the other diameter mark on the string, I put a dot next to it all the way around the poster board every 1/2 in aprox. untill I had a circle. I then cut it out, placed it on my mirror, and put a little sharpie dot in the hole. The paper folding method wasn't very precise, I found this to be the best method for a 16" mirror. Thanks guys

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That looks good to me! I am sure that it is close enough for collimation.
Good luck with getting it perfect, because when you do it sure looks wonderful. I usually get my collimation pretty close each time I go out. Perfection is hard to get but very close is.
Floyd