The fancy serial number checker's "Coolness Index" raises a lot of questions. What does 90% mean, what about 95%, is it worth something?
The Coolness Index was invented by CoolNumbers.com. In summary, the UCI is just a for-fun metric based on "interesting properties" that a number might have. Many of those properties are based on mathematical theories that do NOT apply to collect-ability among the majority of collectors. The takeaway is that a high UCI percentage does NOT guarantee that a note is worth money and conversely, a low UCI percentage can still POSSIBLY be worth money.
Do you want to know which serial numbers are valuable?
We have an article here for you: Types And Values Of Fancy Serial Numbers
If you're interested, here's what the folks at CoolNumbers.com say about their Coolness Index: