For a second or so the needle proceeds smoothly along the dial. I watch its progress while clutching two can-shaped metal devices, wired to the small machine housing the dial. Suddenly, the needle jerks violently.
'What was that?' asks Janet Laveau, head of the UK Office of Special Affairs, the Church of Scientology's PR machine. I'm disturbed and temporarily impressed - the needle jumped just as I was thinking of a friend who is seriously depressed. How could the machine 'know' what I was thinking?
Few people outside the Church of Scientology, which this year celebrates its 50th anniversary, have seen the E-meter. And fewer still have road-tested it at the Scientology Celebrity Centre in Bayswater, London, a stucco-fronted building where the church's many celebrity followers study the religion when in the capital.
The device is said to measure the mental state of a person, allowing the church's teachers - known as auditors - to pinpoint areas of concern. It would not seem out of place on Star Trek. And, to many, the idea of a church erecting specialist centres for celebrities must seem deeply alien.
But then, the church, which for decades has been at the centre of lawsuits and government investigations, is no stranger to controversy.
Now, however, the church has allowed The Observer access to its Celebrity Centre, although it didn't allow photographs. For the first time, a British newspaper could quiz its senior personnel about its finances, beliefs and influence on wider society.
The picture that emerges is of a sophisticated, well-organised church that is a bizarre marriage of Hollywood and hi-tech.
This is largely down to its founder. The religion - and numerous experts agree that it is a religion - was founded by Lafayette Ronald Hubbard, a globe-trotting autodidact who funded his research into what became Scientology by writing a series of best-selling novels.
Hubbard, who died in 1986, credits psychoanalysts such as Freud with influencing his early work, but the 40 million or so words he produced which shape Scientology's teachings today draw on a panoply of interests, ranging from nuclear physics to engineering to anthropology.
Hubbard's influence is everywhere in the Celebrity Centre. His words are written in bold lettering on the walls. Numerous photographs show him as a chubby man with a receding hairline in a tank top and slacks, gazing enigmatically into the distance.
And then there is Hubbard's vacant office. Every Scientology Celebrity Centre across the world has a sealed room devoted to Hubbard, kept vacant as a mark of respect. In London, a sturdy walnut desk, on which stands Hubbard's name-plate, takes centre stage.
But what you won't see on the office walls, or any other Scientology building for that matter, is Hubbard's FBI file. You won't see the letters Hubbard wrote to the US secret services offering his help in the battle against communism. You won't read the letters he wrote denouncing associates as communists, and you won't see the file in which one agent referred to him as a 'mental case'.
And you also won't read any of the negative publicity the religion has attracted, such as the repeated charge that Scientology narrows people's consciousness. Scientologists fiercely rebut such charges, arguing that the church's teachings give its followers a true sense of freedom, empowering them to take control of their lives.
But the government, aware of concerns surrounding Scientology, refuses to recognise the church's claim for charitable status, as happens in a number of countries, including the US.
And yet, despite the negative publicity it has drawn over the past half-century, Scientology has a powerful draw for many people. The church says it has nine million followers in 156 countries. It has 3,700 churches, missions and groups, administered by more than 16,000 staff worldwide. It claims it has 118,000 Scientologists in the UK alone.
Critics dispute the claims. But what is irrefutable is that Scientology has powerful friends who give it global influence. Each year it holds a celebrity gala for the likes of Tom Cruise and John Travolta, which is attended by thousands and makes for great PR. Other celebrity followers include the actress Juliette Lewis and Nancy Cartwright, the voice of Bart Simpson.
Scientologists believe that celebrities wield enormous influence because they are copied by their fans. 'A culture is only as great as its dreams and its dreams are dreamed by artists,' runs one Scientology maxim.
In the US, senior politicians, civic leaders and police officers line up to sing its praises. The church's work on drug rehabilitation and curbing recidivism has earned it plaudits from those in the penal system. 'I know of no other group doing more effective work in combating the problem of drug abuse,' says Chris Brightmore, a retired detective chief superintendent at Scotland Yard, in one Scientology pamphlet.
The actress Kirstie Alley says Scientology's drug rehab programme, called Narconon, 'salvaged my life and began my acting career'. And in terms of formulating social policy, Scientology has had some stunning successes.
A campaign, spearheaded by another celebrity Scientologist, Lisa Marie Presley, resulted in a major backlash against schools injecting children who had attention deficit disorder with the drug Ritalin. The church's applied scholastics programme has produced scores of converts in Africa and the developing world. At least one private school in the UK is also said to use the system.
It appears an impressive track record for a religion started only half a century ago. Its success is down to the fact that Scientology claims to hold answers to everyday problems. Scientologists believe that people strive to be good and try to help them achieve this. Followers like to quote Hubbard's maxim: 'Others talk about a better world. We are making one.'
There is a strong neo-liberal vein, placing responsibility firmly on individuals to help themselves and then help others.
One of Scientology's aims is for followers to achieve a state of 'Clear', when a person loses all fears, anxieties and irrational thoughts. Beyond this, followers can progress to a series of levels about which little is known, simply because few people ever train long enough to reach them.
However a number of ex-followers have talked about the training they received to detach what Scientologists call 'Body Thetans'. These, according to Hubbard, relate back to the 'Xenu incident' which occurred 75 million years ago. Back then Xenu, who was apparently the Galactic Federation ruler, dropped thousands of human souls into volcanoes on Hawaii and in the Mediterranean and then blew them up with hydrogen bombs. The disembodied souls - known as Body Thetans - exist today and produce warped thoughts among humans. Only by following Hubbard's writings, say Scientologists, can they be removed.
For obvious reasons, the church does not like to talk about the 'Xenu incident'. Supporters say it assumes true meaning only after years of study and complain that those opposed to Scientology use it to paint a derogatory picture of the religion as little more than a sci-fi fantasy, akin to Hubbard's novels.
That numerous organisations have taken a dim view of Scientology is no surprise to its followers. They argue that there are scores of vested interests which feel threatened by Scientology's success.
Over the years, the church has used the freedom of information act to produce a vast library of what it says is incontrovertible evidence that official agencies have conspired against it.
'I'm well aware of the controversy and where it comes from,' said Laveau. 'It all started in the 1950s, when Mr Hubbard started Dianetics [the precursor to Scientology]. Our programmes get people off drugs, they stop ex-prisoners committing new crimes. Other organisations get billions in funding and, if they get a 2 per cent result, that's a success. We get between 70 and 80 per cent success rates. Any group that's effective is going to stir up controversy.'
It is also going to make a lot of money. Unlike other religions, followers of Scientology pay for their training, as do schools that want to use its Applied Scholastics programme and those who want Narconon counselling. The fact that many countries have given the religion charitable status helps, but supporters are quick to dismiss claims that Scientology is a giant money-making business. 'An initial course costs just £16. And all the life improvement courses cost under £50,' Laveau said.
Further up the chain, though, the courses become more expensive, something that the church justifies on its website. 'When one considers the cost of delivering even one hour of auditing, requiring extensively trained specialists, and the overhead costs of maintaining church premises, the necessity of donations becomes clear.'
For those who seek enlightenment, Scientology certainly doesn't come cheap. It is estimated that a dedicated follower can spend tens of thousands.
But those who claim Scientology's training has given them greater confidence, inner strength and, ultimately, happiness, are more than willing to pay the price.
As a best-selling pulp fiction writer once noted: 'If a man really wants to make a million dollars, the best way would be to start his own religion.' The writer? L Ron Hubbard.