How is the tournament rating calculated

When does the highest rating change? My highest rating may never be reached again. I have been on the site for over a year and it does not seem to want to drop--which highest rating is used. Not the 90 day for sure. Is it the annual. how often is that calculated?

Tournament Entry Rating is calculated by the formula (CurrentRating + HighestRating) / 2. The entry rating will never drop to more than 100 points below your Highest Rating. I think highest rating is all time highest and changes if you go above that?

The rating used is your highest rating in the past year and is updated pretty much every day.

Thanks. I am seeing the fluctuations now and see how it works. Your help is appreciated.