A bulky telescopic gunsight, originally from an aircraft carrier, is mounted in the middle of the circular floor and trained on a patch of sunlight touching the waves. From her cliff-top eyrie among the gulls at Portland Bill in Dorset, she watches the weather. Every hour of sunshine, every drop of rain - even the height, type and amount of cloud is fastidiously recorded.
Ms Lockyer, 59, is an amateur weather observer - one of an eager band providing crucial information to the Meteorological Office to back up readings from automatic stations and satellites.
Details recorded with pencil and paper in their back gardens and potting sheds end up as hi-tech graphic images on weather charts for airline pilots, ships' captains and television and radio weather forecasters. Indeed, without regular reports from these stations, the weather map for the British Isles would lack important detail.
Ms Lockyer has been studying the skies over her corner of Dorset for more than 20 years, 14 of which have been spent running the Portland station from her B&B at the disused Old Higher Lighthouse.
It is a year since the station went partly automatic and readings for temperatures, wind speed and direction, and barometric pressure began to be taken by computer.
But she still records manually the visibility, cloud conditions, sunshine and rainfall every three hours from 8.45am to 8.45pm, in between seeing to her guests and tending the salt-resistant plants in her garden. Squinting up into the sky, she can identify cloud formations with ease - the result of years of practice.
"The lowest we've got here now is some cumulus over there at round about 3,000ft," she says, pointing north towards Weymouth, "some strato cumulus at about 4,000ft to 5,000ft," - her arm swings round and out towards the Channel - "and all that other white stuff up there is all cirrus between 20,000ft and 30,000ft. Visibility's about 25 miles plus, which is excellent. You picked a nice day."
Nice days here, however, can be rare, and over the years Ms Lockyer and her lighthouse have braved some awesome storms to send back information for the nation's benefit.
"You know about the waterspout?" she asks. "Came in from out in the Channel on the 12th of September 1993 and came straight towards us. If it had come ashore here, this place would have been a mess."
As her photographs prove, the waterspout was a real twister, a bruised grey spiral hundreds of feet high with a fury of spray at its base. "Enough to lift a small fishing boat clean out of the water." As it skirted the Isle of Portland, about 300 yards off shore, she alerted the Dorset coastguard, but shortly afterwards it lost its power and died, minutes before touching land.
Although waterspouts are infrequent, winds of 100mph are quite common at the lighthouse. "You can't stand up in that," she says. "Which makes doing your readings rather difficult.
"When you've got a gale blowing you get a lot of noise, but just before you get one of those 100mph gusts you hear a high-pitched whistle and you know it's coming."
Risk of injury from the elements is a potential hazard of weather watching. Carl Matthews, a 41-year-old observer from north Cumbria found himself dodging thunderbolts to get his readings.
"A storm had passed over and it had just stopped raining when I thought I'd better go out," he recalls. "I remember looking into the Stevenson Screen at the bottom of the field and then there was this flash right behind my back. I thought: that's it, and I ran back inside. I got my readings done, though."
But rather than putting people off, such danger seems to be attracting them to this pursuit of the elements. Earlier this year the Met Office calculated that the number of amateur weather observing stations had dropped by about a third since September 1990, from 122 to 88. Concerned at the number of weather blind spots this was causing around the country, they advertised for more sky watchers.
They expected mild interest - say 50 or so weather buffs with some time on their hands - but were deluged with almost 700 letters.
The success of respondents will depend largely on where they live and how many other stations are in their area. Those selected will be trained by the Met Office, given the latest computerised monitoring equipment and paid a nominal rate (pence rather than pounds) for their trouble.
But what makes these people want to spend up to 14 hours a day measuring the elements to feed the country's addiction to forecasts? "You've got to love your weather," says Peter Loweth, who runs Brede 881, a station near Hastings on the Sussex coast. "I'm very interested in the seasons. I'm basically a countryman at heart. I love a good wind, it's very exhilarating, especially if you are on the cliffs."
To him the British obsession with the weather is perfectly understandable: "It's because we are an island and so much of our trade used to be dependent on the sea. Weather was very important to us."
It still is. To mariners bobbing about in the romantically named sectors of sea around Britain and Ireland, Radio 4's shipping forecast crackling over the airwaves is a lifeline.
Warnings of gales in Fair Isle, low visibility in Malin or a deep depression approaching Stornoway are likely to have been composed from information supplied by observers monitoring instruments outside their kitchen windows.
The BBC's weatherman Ian McCaskill has always relied on these observations coming in from the more remote parts of the country. "I have to confess they have been a blinding revelation," he says.
"There we are in the morning at five to seven, not really knowing what's going on with the weather in certain parts of the country, and then we get a report from an observer. Oh my God, you mean there's snow up there?"
The recent lack of observers has caused him and his colleagues problems with forecasting. "There are now whole counties of the British Isles without observers' weather reports, which is dreadful," he says. "On many occasions the only indication we get of a patch of weather is from these observers. Most of them have been doing this for 30 years, so there's nothing amateur about them."
Although age and experience are not prerequisites for becoming an observer, the Met Office admits most tend to be middle-aged or older and one couple is in their 80s.
But its successful recent recruitment drive will boost their ranks considerably, ensuring that younger observers are on hand to sustain the UK's weather habit for several years to come.