"Look, it's obvious isn't it?" The man asking the question is a welding instructor. He is showing me a weld. That much I know. It is meant to be an example of either a good weld or a bad one. That's the tricky bit.
I have been trained to teach poetry; the essentials of a good sentence; the difference between a comma and a full stop. How to join two bits of metal together in a bond that won't break is another matter entirely. "Yes," I finally reply. "I can see that."
This is what happens when you step outside your comfort zone. And for most of my five-hour tour of the National Construction College's huge 450-acre campus I have been well and truly outside mine.
The NCC is a college - but not as we know it. At least, not as I know it.
For a start, it's located in the middle of nowhere - and then some. Fifteen miles north-west of the Norfolk town of King's Lynn to be precise. If you go much further, you're in the North Sea.
And then it doesn't look quite like any other college either. Probably that's because it started life as an RAF base, and the snake hasn't entirely shed its old skin. Three of the base's hangars are still in use, as are many of the old accommodation blocks. Even the control tower's still there.
Not the runway though. That's been converted into a vast lunar landscape where bulldozers run back and forth, shifting the top soil into new and interesting formations.
What they teach at the NCC isn't to be found in your average neighbourhood tech either. As Chris Barrett, head of access training and my first "tour"
guide of the day, explains, the national college was set up to do the "hard" bits of construction - the specialist, expensive or large-scale operations that more conventional set-ups simply can't handle.
In Chris's domain they certainly know all about that "hard" stuff. For a start, they teach something called "rope access" - steeplejacking to you and me - which involves climbing up, or hanging off, the tallest of buildings. Currently they train 18 apprentices each year in this vertiginous art.
We watch some of them swing about up in the roof of one of the former aircraft hangars. "You need a head for heights," I observe. "That's bloody obvious," Chris might well reply, but confines himself to a polite "yes".
We go outside and watch some more students - or "delegates" as they call them at the NCC - at work. These guys know how to keep a cool head in high places. Hanging from the top of a 100-ft brick tower, they're happily dismantling a complex scaffolding structure - scaffolding being another of the specialisms taught in Chris's department.
At my next port of call it's more about digging down than climbing upwards.
Tony Nicholson, senior instructor in the construction department, introduces me to a group of men standing by the en-trance to a shaft. It might be "only" 15 ft deep, but they're to be put down it in the pitch black and must find their own way out. Oh, and as the exercise supposes there could be gas around, they'll have to wear breathing apparatus.
This, Tony confides, is all part of "confined spaces training", one of about a dozen esoteric skills that his department handles, with qualifications mainly at NVQ level 2 and 3. "Construction" also caters for several hundred engineering graduates each year. Their companies, Tony says, send them to the NCC to "get them dirty" - which I presume refers to the hands-on skills they learn.
But it's in Andy Newell's department that they get to play with all the interesting boys' toys - or heavy plant, as they prefer to call it. Their four tall cranes dominate the skyline, and they've also got another 10 smaller ones, plus a variety of bulldozers, excavators, wield-loading shovels, telehandlers and dump trucks. People come from all over the country to learn to use this kit, which Andy estimates would take pound;10 million to replace at today's prices. At any one time there are around 400 students on long or short courses, both apprentices and adults. Delegates also learn how to maintain and repair plant, which is where I discover how little I know about welding.
But the college - one of five regional NCC campuses in the country - is facing an uncertain future. Plans to sell off part of their site for housing were turned down recently. That has left a hole in their finances that not even the biggest bulldozer can fill in.