The Billion Dollar Question
It's often said there are only three events that are guaranteed the biggest global audiences: Olympic Games, World Cups - and major British Royal landmarks.
We'll find out in the next few days just how much a Royal Wedding unites Britain and the wider world, and this isn't a post that's going to compare relative audiences because we know all three are huge.
But I want to share a few thoughts about the art of viewing figures and then about what links these events in a digital age.
The key recommendation about audience figures is always to have a degree of scepticism.
My favourite was an international event that claimed its total viewership was actually larger than the entire world population by a factor of about 4, but there are many telecasts that like the "watched by one billion" figure.
The Beijing 2008 opening ceremony came close to the billion mark
Similarly with the Super Bowl, which multiple journalists have claimed is "viewed by one billion worldwide" but where there was a challenge from CNN.
An additional point here is that there's potentially a massive difference between "watched live" and "saw". A live audience in the UK to the Oscars is vanishingly low because it's on pay TV in the early hours of the morning; but in fairness more will see the clips of the winners making their teary speeches in later news bulletins on BBC, ITV and Sky.
Even then some figures don't add up. There was this piece in 2007 saying that "one billion" (that number again) had watched Arsenal v Man United at the Emirates.
Now, a typical Premier League live audience in the UK is around 2 million - and the highlights on Match Of The Day will reach a further 4 million.
News bulletins showing the goals might add the same again. But you still only get to maybe 20% of the UK population seeing the key action, so it stretches credibility to expect it to reach a total of one thousand million people globally - especially given the relative lack of interest in football in markets like the United States or India.
The line to be wary of is an estimate of how content is "available" in a certain number of households.
Most of us now have a choice of hundreds of channels in our home but we watch only a handful.
So "being available" and "being watched" are not the same thing, and almost nothing is watched live by a billion people.
The most credible candidates are the Beijing Olympics opening ceremony - which had an "audited" figure just a little below that - and the funeral of the Princess of Wales, which is usually estimated to have been watched by around 750m.
As for what links these kind of events: what we can see is that audience behaviour is going in two ways.
On the one hand, there's more fragmentation than ever before - more personalisation, more choice, more channels, more content you create yourself.
On the other hand, people still seem to crave those moments that unite and where you feel part of a bigger experience - and in the UK that can be anything from Strictly Come Dancing to the major sporting moments and Royal ceremonial.
Here at the BBC it's one of our central commitments to the public that we're the place where as many as possible of these events are experienced free-to-air by the greatest numbers.
Our research suggests that people still want a sense of community amid the vastness of digital space, and if we didn't have these common experiences then our belief is we'd all be the poorer.
It's something we'll be putting to the test both this week - and for pretty much the whole of next year.