Did you know there are six million rivets that hold the Sydney Harbour Bridge together? No? Bob Dawson does. That is not all Mr Dawson knows about the bridge. He knows that the arch span is 503 metres; the length of the bridge is 1,149 metres; the total weight of steelwork is 52,800 tonnes; and the height from sea level to beacon top is 141 metres.
In fact there is very little Mr Dawson does not know about the bridge. He is a veritable walking - or, in his case, climbing - encyclopaedia of one of Australia's most recognisable sights.
It is Mr Dawson's job to know. He is one of a group of 40 tour guides that daily troop hundreds of people to the top of the Sydney Harbour Bridge, giving them a step-by-step history while treating them to an overwhelming view of one of the most stunning cityscapes in the world.
Mr Dawson says he has climbed the bridge about 150 times since the company, Bridge Climb Sydney, was given permission to conduct tours last October. The embarrassingly fit 60-year-old says every climb still carries the same fascination and excitement for him as the first.
In its short life so far, the Sydney Harbour Bridge climb has become one of Australia's most popular tourist attractions. Since October, more than 80,000 people have zipped themselves into gun-metal-grey coveralls to match the colour of the bridge and trudged to the top.
On a perfect early autumn Sydney morning, the 360-degree view - which takes in the Sydney city skyline, the majestic Sydney Opera House, the botanical gardens, the islands that dot the beautiful meandering harbour, the Tasman Sea, the Glebe Island Bridge which because of its shape is known as Madonna's Breasts (her pointy metal ones), and the hazy Blue Mountains 81 kilometres away - is intoxicating.