AirSense 11 "Extended Period" readout

In the My Sleep View readout on the AirSense 11, the first choice under Addition Info is "Extended Period."It gives the number of hours used, but the third item down is "Leak." That is very different from the number given under "Usage." For instance, Leak in Usage may be 7L/Min. while in Extended Period it might be 20L/Min. Anyone can tell me how these numbers are obtained and what they represent?

See if this video helps you...https://www.youtube.com/watch?v=9x-7xkqnqeI

Thanks, that video was very informative! It didn't cover the "extended period" readout, but I found, on looking at the readout again I had missed the line "12 month period." So it is an average over 12 months!