The two parts of the equation are:
Equities = SPX
Borrowing Rate = (US10Y + 1 + 1/US10Y)
Their product is basically the "true" change of the economy. It answers how much the economy is growing/dropping.
Equities * Borrowing Rate
While their ratio is the relative increase of the two. It answers how much equities are increasing compared to the increase of "fake money" made by "duplicate-lending".
Equities / Borrowing Rate