IndexRank is a 0-10 metric (higher is better) that uses an algorithm based on Google's indexing data to determine the indexing rate of a website.
What does IndexRank measure?
IndexRank measures the rate at which your site is being indexed, which also translates into the rate at which it is growing. If you have a stagnant site with little content being added, you will have a low IndexRank. If you constantly increase content, you will have a high IndexRank.
How can I improve my IndexRank?
In order to improve your IndexRank you must consistently add content to your site. One of the easiest methods is to incorporate a blog, but you can also write or buy unique content and grow your site week after week, month after month.
How it works
This tool collects Google indexing rate data for different time periods. If your site is less than a year old, you can expect your IndexRate to be lower. Data is cached on a weekly basis, so changes in an IndexRate would only be seen at a minimum every week. Basically, you don't need to check it every day.
For more info, see the announcement of IndexRank
and Aaron Wall's post about google's data filters