It was a secret that followed George Harrison to his grave: what exactly was the opening chord to The Beatles' song "A Hard Day's Night"? Perhaps no four seconds of music have ever received such scrutiny. 

Over the years scientists, physicists and musicians have all attempted to decode the mystery. Was Harrison doing all of it? How? Did Lennon chip in? Was McCartney playing a full bass note or a harmonic?

Four years ago, Professor Jason Brown analysed 29,000 frequencies to come up with the closest approximation to date: an A,D, G and C on the middle strings. But now Dr Kevin Houston from the University of Leeds claims to have trumped the Professor with a more complex equation: an Fadd9 on a 12-string electric, with the bottom E pressed at the first fret and Lennon doing the same. The debate rages on, but it's good to know that some of the smartest minds of our generation are dedicating themselves to such a singular, important cause.