Try as you can, sometimes a typo gets through all the proofing and editor and review checking.

Unfortunately that has happened with page 48 of QLBB 3rd edition.

Part way down there is an equation that reads:

Screen Shot 2017-08-20 at 13.02.32

when it should actually read:

Screen Shot 2017-08-20 at 13.04.48

sorry about that folks and thanks to Don Musick and David Capstick for pointing the mistake out.