About two hours after Nvidia sent investors around the world into a fresh frenzy over artificial intelligence, Australasian accounting software group Xero delivered an impressive earnings beat thanks to a decidedly old-school tech rule.
Developed in about 2015, the rule of 40 says that a software-as-a-service company should aim to deliver annual revenue growth and an annual free cash flow margin (free cash flow divided by sales) that adds up to 40.