BTW, in using that forumla, no value can be zero or negative. That has seen me through 52 years with the same lady, so I know that formula works. At least for tools. An a tool (when explaining it to the wife) is anything that can be used to make money. Doesn't matter if it ever does, just so long as there's the potential.
You're right!! And over the years I've bought a lot of tools - from her, not so much as a whimper. I had a wee little accident with the Husky airplane in my avatar, back about 15 years ago (no hull insurance, so I was gonna take it on the chin). Stuck at a strip with no roads, got rescued by boat. That evening, she asks, "So what color is the new one gonna be?" YES!! Now I remember why I married her!