When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I think it's just a reference dot to help give you an idea of how far off the full mark you are when it's dark and you can't see how many lights are off.
Just a little easier to see the gap between level and the dot. Could also count the ticks and just know how many there are total, but I don't think the average person is that detail oriented.