March 1994. It occupies almost the entire ground floor of the Waterloo Block (formerly a barracks) and is designed to allow up to 20,000 people a day to see the collection of more than 100 priceless objects and 23,578 diamonds, rubies, emeralds and sapphires. They were lit by state-of-the-art fibre optics and rested on French velvet. However, critics derided the experience as "just an exercise in crowd management, beautifully lit and presented but literally mechanistic", a reference to the six-inch-thick, two-tonne steel doors, and the use of a travelator at peak times. Present day In 2012, the exhibit was given a £2.5 million revamp to include a new introduction area with a video showing the history of the Crown Jewels and explaining how they are used in the coronation ceremony. The jewels themselves are displayed in the order they are used in the ceremony, and Handel's coronation anthems can be heard as visitors tour the exhibition. Brighter lights were installed to present the jewels in a more natural way, and a new lift provides disabled access to the viewing platform. The Princess Royal officially reopened the Jewel House on 29 March 2012. The underground vault built in 1967 is home to 25,000 architectural drawings of historic royal palaces. Security The Crown Jewels are protected by bombproof glass, and visitors to the tower are closely watched by more than 100 hidden CCTV cameras. The security of the Tower of London as a whole is provided by the 22-strong Tower Guard which has been at the Waterloo Block since 1845. They are on detachment from the British Army and "operate under orders agreed with the Ministry of Defence to ensure the security of the Crown Jewels". The 38 Yeomen Warders, ex-military personnel employed by Historic Royal Palaces, also provide security, though their daytime role is more concerned with managing the large number of visitors. Unlike the soldiers of the Tower Guard, who rotate, the Yeomen Warders are permanent and live in the tower itself. The present body dates from 1485, and they wear similar uniforms to the Sovereign's bodyguards, the Yeomen of the Guard, of which they have been extraordinary members since 1550. The jewels are removed on the authority of the Lord Chamberlain, head of the Royal Household, exercised by his deputy the Comptroller of the Lord Chamberlain's Office. He signs a voucher on receipt of the items from the Deputy