Trying to predict the numbers is always difficult. The issue involved. The levels of anger it has generated. Then, even the weather. On a brutally hot summer's afternoon in Hong Kong, especially the weather.
As the given hour for the start of the protest against Government plans to introduce compulsory national education approached, small groups of parents and their children emerged, sheltering from the sun under flimsy umbrellas. It looked like the organisers' predictions of 5,000 to 10,000 would barely be realised.
But as the first of the marchers were well along the route from Hong Kong's Victoria Park, it soon became evident that the throngs who were converging on the starting point far outnumbered those who were setting off. This was going to be a big one.
Hong Kong has had its share of big ones. The old perception of this moneyed city as apathetic, more interested in making a buck than making a point, died with the thousands who turned out in torrential rains to mourn the dead of the Tiananmen Square crackdown in 1989.
Public dissatisfaction with the Hong Kong Government in 2003 brought half a million people out onto the streets. It led to the withdrawal of a controversial piece of legislation, the resignation of a senior minister and arguably speeded up the early retirement of the then Chief Executive.
The political barometer that is the street protest – for without full democracy, the city must rely on such indicators as a measure of public discontent – has waved back and forth in the intervening years. Sometimes an issue that you thought would galvanize opinion brings out just a handful of activists.
But recent protests - such as the several hundred thousand who attended the July 1st rally, coinciding with the inauguration of a scandal-bound leader many suspect of being Beijing's puppet, and yesterday's turnout of 50,000 plus - point to increased tensions in the often-troubled relationship with Beijing.
Suspected political interference from the Mainland is one thing. When that meddling is perceived as an attempt to indoctrinate in the schools that are so cherished in every Chinese community, then it is time to get your umbrella out and put the kids in the stroller.
Organisers say 90,000 turned out yesterday. Police put the figure a lot lower. But supposing we split the difference and settle on 50,000. As Hong Kong commentator Stephen Vines astutely points out, extrapolate a figure like that from a city of seven million to a country like the US, and you would be a facing street protest in excess of two million. That is a massive show in anyone's reckoning.
It is Hong Kong's great irony. A sophisticated place with a well-developed civil society, but when it comes to political development, it is hovering somewhere around the feudal relegation zone in the world's democratic league table. In other places you might write to your elected representative. Get the chance to change that person with a periodic cross on a ballot paper in a far more civilised air conditioned polling station. For now, the sweltering march with kids in tow will have to pass as having your say. And at the end of that trek, the eternal question: Is anyone listening?