Leaning Tower of Pisa is now one inch straighter

(CBS News) It's not visible to the human eye, but the Leaning Tower of Pisa isn't leaning quite so much these days. In fact it's actually straighter than it has been for centuries, by about an inch.

The change has taken 12 years, the result of a monumental reconstruction project.

The $40 million spent to save the tower from what many saw as imminent collapse is good value for the money, according to technical director Giuseppe Bentivoglio.

Bentivoglio told CBS News' Allen Pizzey that the tower should be stable for a while.

"For the next two or two-and-a-half centuries there will be no need for another intervention," he said in Italian. "This is for certain."

The name Pisa dates from about 600 B.C. and it's ancient Greek for "marshy land," so it's no surprise that one side of the tower began to sink shortly after construction began.

The engineering project to correct the tilt involved attaching cables and enormous lead weights as a counter balance, then extracting soil so the structure would settle back.

Now, lawns and walkways cover the extraordinarily complex engineering work, but the tower's statistics speak volumes for the accomplishment. Construction began 600 years before the U.S. Declaration of Independence and took two hundred years. At 180 feet, it's barely one-third the height of the Washington monument, but it weighs 14,500 metric tons, roughly the same as the Brooklyn Bridge.

It's classed as one of the seven modern wonders of the world and the lean is what makes the tower more than just another magnificent example of ancient architecture.

More than 500,000 visitors a year gasp their way up the nearly 300 stone steps that spiral to the top, unaware that the tower actually moves all the time.

"It's sensitive to the temperature and the wind" said Bentivoglio. "Especially to the underground layer of water, which varies depending on the season."

Even if you could feel the movement, however, the stupendous views make up for it. And for those who get the timing right, one of the seven bells that represent the notes of the musical scale will chime.

Fortunately for the sake of the tourist's hearing, only one the bell is rung electronically. The sound of all seven would make the human body and the structure vibrate.

The tower is the crowning glory of a piazza known as "The Field of Miracles" which may seem like something of a local conceit, but then again given the available evidence maybe not.