TitleZ is an app that gives rank and charts sales rank by its highs and lows. You can see your current rank and then averages for 7-days, 30-days, and 90-days.
TitleZ is easy to use. Though it's difficult to attribute a specific promotion to increases in sales, with this app you may be able to correlate some specific promotion push with a sales spike. You can also generate a printable report for each book.
Remember what A. A Milne said, "Almost anyone can be an author; the business is to collect money and fame from this state of being."