The Fraction of Everything Index, or FOEI, is a way of measuring how much of "everything" a verse has. In other words, it is an existence index.
In FOEI, 0 means it contains nothing and 1 means it contains everything.
Also, an FOEI of (0, 1) means it contains something but not nothing, but an infinitely small fraction of existence.
For example:
Protoverse has an FOEI of 0, since it contains absolutely nothing.
Universe has an FOEI of (0, 1) since it contains only a infinitely small part of everything.
Multiverse has an FOEI of (0, 1) since it still contains only a few things, even though it contains more than the Universe.
Omniverse has an FOEI of 1, since it contains everything that exists.
There are some areas where it contains everything that exists AND more, like in The Box, which has an FOEI of Omega.
If it had an FOEI of 2, it would contain everything, as well as another quantity the same size of everything, sort of between existence and non-existence.
You can also take the (0, 1) and convert it to (1, 2), which is everything and some part of another space relative to everything.
The larger the FOEI is, the more it contains, even though it contains everything AND more.
With natural sized gaps, we could create unimaginably large verses with this index as well. This can be used if the EUSI scale isn't enough, or if you want to have a fraction of everything or more than everything that size cannot quite justify.