How is the monthly growth for Signal Stats calculated?

 
How is the monthly growth of a Signal calculated? For example on <Deleted>
 

It may be written on the first post of this thread:

Frequently Asked Questions about the Signals service
Frequently Asked Questions about the Signals service
  • 2013.02.20
  • www.mql5.com
Discover in 15 Minutes: Watch the Video about Trading Signals in MetaTrader 4 and MetaTrader 5 The most frequently asked questions related to the S...