A system that doesn't move a number is a hobby. We try not to build hobbies. So every system we ship is tied to one of three numbers, agreed before we start.
Hours saved. The simplest one. How much manual time did this remove, per person, per week? We measure it before and after, and we don't round up. If it saved four hours, it saved four hours.
Revenue recovered. Leads that used to go cold and now book. Old contacts that used to sit in a spreadsheet and now come back as appointments. This is the number that pays for the rest.
Deals closed or time to close. Faster replies close more deals. Shorter cycles close them sooner. We track the one that fits the business, and we watch it move. If it doesn't move, we didn't earn the next project.