Set your 12 o'clock position with a level... because

[Jayster]

This is another method that’s been discussed and that I have used in the past.

How To: Setting Sprocket to 12 o'clock Position

@blurfl posted his method of aligning the sprocket to 12 o’clock… I’m summarizing it here: Use either your chain (or perhaps a spare piece of chain) and drap it over the sprocket. Take a string level and insert a piece of straight, stiff wire through the holes in the level. @blurfl used a section of a clothes hanger. Place the level in between the two sides of the draped chain with the wire poking through the gaps in the chain, as shown below. Use the software to adjust the orientation of t…

I do like your method though with the level on the two points. I wonder since they are so close if you can dial it in accurate enough.