Axioms
Boots and Satchel, Ready to Go
Boots and Satchel, Ready to GoA worn leather bag and heavy walking boots wait by a cottage door in a rainy night market, glowing with lanterns. They've been used and will be used again—tools that earn their keep with every journey.
Jo = Use ÷ Pri
Spend on what lasts

The joy you get from a purchase is how much you will use it divided by its price.

The idea

Buy what you will use Money spent on things you use every day keeps paying back. Expensive things that sit unused cost the most.

Why this form

A ratio: an expensive thing rarely used gives the least joy per coin.

Symbols

JoJoy per coin lasting value for the money
0 = regretted, 1 = loved for years (0-1)
UseUse how often you will truly use it
0 = once, 1 = every day (0-1)
PriPrice its cost against your means
0.1 = trivial, 1 = a big stretch (0.1-1)

Checks

Make a formula from any post