Perhaps you are referring to the GRM (Gross Rent Multiplier)?

Calculate vacancy this way...based on what actually happens:1 - Find out what the vacancy rate is for your units (this isn't a "%", it's a number of months per year.2 - Calculate what you would need to cover per month when a unit is vacant....i.e..Taxes, Gas, water, Ins, Snow (if Winter...figure it would be), utilities, D.S3 - Multiply your answer in #1 x your answer in #2.4 - Take all of the positive cash flow in the first months, and put it into a reserve, until the reserve totals your answer in #3.Now your are actually got your vacancy covered.CAPEX is another matter. 

Multiply your total footage by 500 to get the total BTU output to the space at 180 degree water temperature.

I'm just trying to understand the use of the "60" multiplier above and whether it makes sense in this case?

From what I researched, depending on the multiplier used, this should represent 60-80% of the appraisal value (which had me stoked!).  

I thought Sq Ft of the property multiplied by .05 might be a decent quick monthly back of the napkin estimate.  

Whatever you think your rehab timeline will be, multiply it times 2.5. 

Find a deal and have the willingness to do whatever it takes to get it done and you can multiply your money pretty quickly.

Multiply by 6 and factor the $1200 into the expenses of the deal.

Multiply this by periods 360 = a total payment over 30 years of $569,747.41.