GHow is SOC (strength of Competition) for MNF Calculated?

I understand the 3 queries that go into finding the SOC of a keyword.

But how are these 3 values turned into one number....for instance in the image below. How are the 3 used to calculate the figure of 19?

Add or subtract and divide? Can someone please shed some light on the formula?

 

On a side note, have you noticed the keyword searches in MNF are pulling back fewer suggested results lately?

 

maybe has to do with the new tool.....which totally stinks in my opinion

 

I know, I use to get hundreds of keyword suggestions, not I get like 30 per search.