What does Gross Rent Multiplier

[RJ Emmett]

Hello, 

Newbie here.  I was searching through the RMLS and trying to get some practice in on looking at buying a rental property.  I'm not ready to buy, but I am pretending that I am to gain some understanding on how to figure out what is a good deal and what is a bad deal.

I came across several listings with Multiple unit buildings with a line in the description, "Gross Rent Multiplier".  This particular building was a duplex with each unit at 3bed, 2bath, 1500sq.  The Gross rent multiplier was 31.24.

Can someone explain what Gross Rent Multiplier means?

Please and Thank you's in advance!