On a whiteboard inside Facebook’s sprawling Menlo Park campus, Sara Su is drawing a diagram to explain exactly how its News-feed algorithm decides what you see.
"The goal of this algorithm is to figure out from all of the stories that we might be able to show you when you open up Facebook, what is the most personally meaningful, personally relevant?"
This ranking algorithm provides the instructions for one Facebook’s most important and controversial problems - what to show you.
Sara Su says explaining the algorithm’s inner workings are Facebook asking users to trust it again.
"We’re in it for the long haul. Trust can be lost in an instant, but it takes time to rebuild."
The algorithm looks for what users engage with - signals, Ms Su calls them, such as which posts you and people in your friend circle like, share or comment on.
"For each of these stories we look at hundreds of thousands of signals. It could be who posted it - was it your friend, was it a page that you follow, when was it posted? - we know people care a lot about stories that are fresh, and there might be other things like, how many people have liked or reacted to that story, how much engagement it's got so far. We can use these signals to make a series of predictions, best-guesses about different ways this story might be meaningful to you."
She says they simply score each story’s relevance.
"From all of these signals and predictions, we come up with a number and we show you the highest-scoring stories first."
In January, the company announced a re-design, promising to show less news or click bait and more posts from friends and family.
There were howls of protest from business pages and viral hoaxes suggesting the news feed would now only show you posts from 25 friends.
Sara Su says its actually designed around what Facebook founder Mark Zuckerberg calls "meaningful social interaction".
"We’re weighting stories that are more likely to spark conversations. That will result in them numerically getting a higher relevance score and they’ll start to show up earlier in people’s news-feeds."
But what does this have to with Facebook’s trust problem?
The revelations in March - that Facebook knew but hadn’t acted on Cambridge Analytica’s misuse of Facebook users' data - reignited the still- smouldering scandal of Russian interference in 2016’s presidential election.
And it again called into question the ethics of social media companies whose business models were based on gathering ever-increasing slabs of their customers' attention.
Younger users in particular turned off, and Facebook’s share price plummeted.
Paul Verna, an analyst with the firm E-Marketer, explains why trust and Facebook's fortunes are so closely linked.
"There is a fundamental truth that trust is the real currency that all these platforms depend on ... because without that you can’t build the social network and you can’t attract advertisers."
The United States' first midterm elections under President Donald Trump are due in November.
SBS was granted access to observe the social media giant’s efforts to prevent itself from being a platform for election manipulation, misinformation or hate speech.
Monika Bickert is in charge of Facebook’s content policies - its rules for what people can say.
"The more we can tell people about what’re doing to draw the lines on speech and to enforce those lines, the better. You can go to our site and you can see the same guidance that we are giving our reviewers."
Observers, like Stanford University social media lab professor Jeff Hancock, say Facebook’s and other tech giants' policy of transparency is also motivated by a fear of legislators in Washington.
"Here in Silicon Valley, regulation is kinda like a dirty word. The clock’s ticking (time is running out) I think, and unless they start demonstrably doing better at dealing with misinformation, manipulation, all the way to things like bullying, the more likely it is the government will step in and regulate."
Facebook’s response has been huge investments in teams of content moderators and machine-learning technology.They’ve helped it remove over 580 million fake accounts in the first quarter of 2018, and take down over 650 Iranian and Russian-backed pages for what it calls "coordinated inauthentic behavior".
But Facebook’s Monika Bickert acknowledges those stats alone won’t convince people
"We’re definitely getting better at finding this sort of activity and stopping it… "
(reporter) "But are people recognising that?"
"In terms of communicating with people I think there’s more we need to do."
Facebook won't say how users are responding but a new survey released this month by the Pew research centre backs that sentiment.
Over half the adult Facebook users in the US still don’t understand how the news feed works, and in the last 12 months nearly three quarters have either scaled back or stopped using Facebook.
The company's harshest critics believe Facebook is reaping what it has sown (feeling the consequences of its own actions), seeing its present problems as the consequence of pursuing growth at all costs.
But staff like Sara Su believes that by acknowledging wrongdoing and working to atone for its mistakes, Facebook can recover.
"It's always hard to read negative press about the work that you’re doing. But I think that really underlines for all of us on this team how important this work is, and that keeps us going every day."
