What does Apple's 'do not track' option mean for users and advertisers?

Apple's latest operating system upgrade is offering users the chance to opt out of being tracked by the apps that they use. The iPhone maker says the changes will give people more control over their privacy, while advertisers - including Facebook - have complained that it is an abuse of Apple's market power. Also today, we look at the latest financial results from the bank HSBC and the electric carmaker Tesla, both of which have seen profits rise in the first three months of 2021.