Line 83 is ‘Gain/Loss-to-Lease’. This is a concept commonly seen in modeling short-term leases that tracks the difference between asking rent and actual rent at a property. Spencer uses the concept here to track both potential rent vs actual rent in order to calculate economic occupancy (row 72), as well as track the difference between in-place rents and market rents.
Or in other words, during lease-up the Gain/Loss-to-Lease line, in this case, tracks the amount of actual vacant space so as to compare Total Rental Income to Gross Rent (i.e. economic occupancy).
So if you open up a fresh copy of the model, you’ll note in column Y that Gross Rent (i.e. Rent as if property was 100% occupied) = 63,950 where as ‘Gain/Loss-to-Lease’ = (57,555). What this is saying is that the property is only 10% leased (1 – 57555/63950). As the property leases up (see row 71), the ‘Gain/Loss-to-Lease’ decreases to the point where it is only tracking (at stabilization column AI) the difference between in-place rents and market rents.