I may have mentioned this to you before but due to the effect of Earth's gravity, in order to obtain a pendlum cord that beats for precisely one second at the latitude of Giza requires a pendulum cord to be a little over what we know today as 39 inches. By using Earth's gravity and its rotation we can uncover how the Inch and the Royal Cubit may have come in to being. You can read this in more detail in The Gravity Cubit.
It is curious also that the AEs used a little over 39 degrees as the inclination for the shafts of the Queens Chamber. It would seem that the number 39.x was clearly of some significance to the Ancient Designers of Giza.