SaaS METRIC OF THE WEEK: Churn.
See #2 for more on Churn. According to CatchJS, though, we're all calculating churn rates wrong. If you love Statistics, the article is well worth reading. It even gives some Python code to perform the more complicated probability-based equation they recommend. You can then check this tool(as a handy Google Sheet) from Newfund to analyze the strength of revenue streams for any B2B startup. A complimentary article outlining the methodology behind the tool is here (and you should read it first).