"78 countries worldwide have run the story. The latest was Costa Rica."

Andrew Barnes' four-day working week experiment in late 2018 at the legal services company he leads has made him famous globally.

"At one point, the Perpetual Guardian four-day week was the most-read story in the New York Times after the Trump/Putin summit," said Barnes.

In the past week Auckland-based Barnes, whose book The 4 Day Week has now gone on sale, was interviewed by reporters from the US, the UK, France and Bulgaria, and media in Turkey have now become interested.

The book tells the story of Perpetual Guardian's experiment, and subsequent permanent switch, to a four-day working week.

Perpetual Guardian was a wills, estates and trusts legal services company, and while not everyone in the company had decided to work for just four days a week, those who wanted to could, providing they were productive enough to justify them.

he idea came to Barnes on a long-haul flight from Auckland to Doha, during which he read an Economist article on research showing workers were typically only productive for 1.5-2.5 hours a day.

"I worked out the maths," Barnes said. "My theory was if each of my employees was productive for an average of about 2.5 hours per day, then as an employer I only needed to claw back 40 more productive minutes per day to get the same output from staff in a four-day week as in a five-day week.

"If I succeeded, productivity would remain steady and so would profitability. What I could not predict was how a 'free' day off each week might affect staff well-being and attitudes. This was the inception of what we now call the 100-80-100 rule.

"Staff receive 100 per cent of their contractual compensation and need to work only 80 per cent of the time, provided they deliver 100 per cent of the agreed productivity."

The Perpetual Guardian experiment reported around the world, including in countries Barnes would not have expected.

"We've had a large amount of books going to India. I didn't really think that was where this was going to go," he said.

Barnes believed the four-day working week idea had universal appeal in a world in which people everywhere were struggling to juggle the demands of work, travel and family.

"Everywhere you travel, everyone is in the same boat. We are over-connected, over-worked and we need two salaries," he said.

People were increasingly crammed into mega-cities, where commutes were dreadful, and housing expensive.

"It doesn't matter which country you are in, you get the same thing," he said.

Barnes believed the appeal of the Perpetual Guardian experiment was partly due to the scientific rigour it had, as Barnes had independent researchers track the eight-week trial, and gather data.

The results convinced Barnes that the five-day week was a nineteenth-century construct that was not fit for purpose in the twenty-first century.

He and his partner Charlotte Lockhart set up a not-for-profit community foundation to promote the idea around the world, and planned similar organisations for the UK and the US.

The four-day working week concept was challenging for people to get their heads around, and challenging for workers to get used to.

In workaholic Japan, efforts to get people to work fewer hours, sometimes had to be coupled with training on what to spend the time on, Barnes said.

"They actually had a programme to help you work out what you did with your family. We are not as bad as that. We do not have a word for dying of overwork in the office. But we had people who said they didn't know what they were going to do with their time off. It was really quite bizarre we had that issue."