The UK's tallest mountain has been re-measured and it's now officially an extra metre taller. Thanks to more modern measuring technology, the mapping agency Ordnance Survey now records Ben Nevis in the Scottish Highlands as 1,345m tall and not 1,344m tall. The last time that the mountain near Fort William was measured was in 1949 when surveyors had to rely on multiple measurements taken from trigs. (This year marks the 80th anniversary of the trigs in Britain.) The official increase in height is not the result of a geological movement but was discovered following the restoration of the trig pillar on Ben Nevis, when OS took the opportunity to re-measure the mountain. The change in height is down to the technology OS now uses to survey and measure giving greater accuracy than when Ben Nevis was last surveyed. In the 1940s, mountain heights were recorded using a "triangulation system" based on trigonometry. Back then it took a team of seven surveyors 20 nights to obtain their calculation. The new measurement took just two hours and was achieved by positioning a geodetic survey grade GPS receiver at the summit of Ben Nevis, which communicated with satellites orbiting the earth. [caption id="attachment_19188" align="aligncenter" width="600"] Walkers head towards ben Nevis.[/caption] Mark Greaves, Ordnance Survey’s Geodetic Consultant, was the first person to discover Ben Nevis had grown. He says:  “The new height relates to the highest natural point on the summit and was measured as 1344.527m. I double checked everything and asked others to do so too. "What is amazing is how close the surveyors in 1949 were. The measured height has changed by centimetres, but those centimetres mean we now need to round up rather than down. So that’s why Ben Nevis will now be officially known as 1,345m.” Field Surveyor Angus Hemmings was one of three surveyors who climbed Ben Nevis to take the new measurement. He says: “We were asked to check if the recent repair work to the cairn had affected the position of the trig pillar, and this provided us with a sensible opportunity to resurvey the summit. “It was raining, sleeting and snowing at the summit, but harsh weather doesn’t affect our equipment or readings. What it did do though, was give me a greater sense of respect for the 1949 surveyors. "Each day they hauled 200lbs of equipment up Ben Nevis and its surrounding mountains. They also had to wait until night because strong lights were shone from the trig pillars of the other mountains on to Ben Nevis, which enabled them to collect their data. “It took the surveyors 20 nights because they only had three clear nights in that period to get it right. To do the best possible job it had to be run with military precision. Their effort and accuracy is remarkable.” OS maintains up-to date-maps for the entire country, holding up to 460 million geographic features in its database of Great Britain. Over 10,000 changes take place each day in what is thought to be the largest geospatial database of its kind in the world, providing valuable information to government, business and citizens. The new height for Ben Nevis will be seen on OS paper maps, starting with the OS Landranger map series. Users of OS’ digital map service, OS Maps will be able to see the new height on OS Landranger and OS Explorer maps immediately, as updates in the geospatial database can feed across multiple digital products. You can visit ben nevis at the end of the West Highland Way walking holiday.