Website Non-Availability measures the time that a website is not available. Downtime is calculated for individual URLs but multi-step processes such as shopping with card payment or user registrations can be identified as 'non-available' if one of the steps is not functioning. The software automatically verifies the server status, downloads the full HTML content and measures the response time of the specified website.
This indicator will be included in my book: Key Performance Indicators - the 100 measures every manager needs to know, which contains an in-depth description of this KPI, as well as practical advice on data collection, calculations, target setting, and actual usage.