Release It! - Chapter 13.1 Gathering Availability Requirements

The proper way to frame the availability decision is in straightforward financial terms: actual cost vs. avoided losses.  If 99% uptime results in 500 minutes of downtime, how much does that translate into lost revenue?  If your system earns $1000 an hour then you have the potential of losing $8000 per month due to down time.  Given that math, does it make sense to pay for making the system %99.50 available?  In short, do the math or you might be paying for something that doesn't give enough in return.  Hopefully, somebody in the company can tell you what the system earns per hour or it makes the calculation difficult.