Friday, 15 April 2022

Accurately, precisely

Back in the day, my teenage brother, adding to his many other talents <grrrr>, won a couple of medals in inter-school target shooting competitions at The National Rifle Association NRA at Bisley near Woking, Surrey. This is a completely different crew from the USA's NRA prising guns from the cold dead hands of Charlton Heston <Not!>. A good shot needs to have a quality gun, a steady hand, a good eye and the ability to pay attention to, and adjust for, external conditions: especially wind speed and direction. 

There are two ways in which you can be off target. If your spread is precise [all close together] but inaccurate [as LL] then the shooter's internals are probably good but some adjustment need to be made to a) adjust the rifle-sights or b) account for wind or c) both.  In the LC "accurate not precise" case, the gun is correctly tuned but the shooter is having an off-day or is just not very good at the task. You will note that in neither case are any of the bullet holes near the bull's eye: and big game hunting is, at this time, ill-advised. If your result is neither accurate nor precise, then you should take up tiddlywinks before someonething gets killed.

Five years ago, I had occasion to be quite dissatisfied with Simon Winchester's book about The Atlantic. Luckily I'm not judgmental and/or hava short memory of previous duds because another Winchester volume was my current audiobook on Borrowbox. It's called Exactly because that sidesteps the issue of defining precision and accuracy which are entangled in most readers' minds. The book won a prize in 2018. The trope is that each chapter embraces a new finer level of exactitude as we move from steam engines to detectors of gravitational waves. Steam engines require that a piston moves up and down in a cylinder; and the efficiency of the machine depends on how close is the fit. The key breakthrough was a boring machine invented by proto-industrialist and iron-master John Wilkinson. The Wilkinson company cut its teeth reaming out the bores of cannon. This made a lot of money because the market for cannon was inexhaustible; and cannon that required less powder and did not explode in the wrong direction were much in demand. It was an obvious extension of the principle to bore cast-iron cylinders for piston engines. Wilkinson guaranteed his product accurate to <gasp> 1/10th of an inch = 2.5mm - the thickness of an old shilling.

Wilkinson reflects on the pursuit of ever more sensitivity because we can; and we can because the nano-engineers are in a perpetual cycle of competition to go smaller. Computers can now store unimaginably vast amounts of information on tiny chips . . . and we fill up the space with really crap photos and uncountable personal copies of the latest hilarious kitten-meme. The scientific triumph of detection is the LIGO interferometer which this I firmly believe measures the gravitation waves predicted by Einstein's theory of general relativity. A couple of billions dollars has enabled the Ligoistas to clock the collision of two black holes a billion light years away. It's not clear what can be done with these data. When cranked to the max LIGO can detect a change in distance between its paired mirrors of 1/10,000th the width of a proton! This is like measuring the distance to Alpha Centauri (4.2 light years away) to an accuracy smaller than the width of a human hair.

One of the more interesting middle chapters is about the development of jet engines by Rolls-Royce. The 30-something son of a long-term pal is an engineer with Rolls-Royce; so he may have a part to play in making the turbine blades which function at a temperature well in excess of what it would take to melt the super-high-temperature alloy from which these palm-sized blades are manufactured. Actually manufacturered has long since become a misnomer because these things are untouched by human hand. Turbine blades can be made to work in these hellish temperatures if their surface can kept "cool" - only 500°C. And they are cooled by leaking a film of lower temperature air from their core to the surface through a pattern of microscopic holes 'drilled' by a computer driven laser. Clearly, holes are going to adversely affect the structural integrity of the surface so it is a delicately balanced optimisation problem.

Maybe it's the audio medium, maybe my ear is now tuned to the Winchester style; but I found Exactly compelling listening.

At the end of the last week, I was nearing the end of Exactly on Borrowbox when I was abruptly closed out of the system. So I don't know how it ends . . .

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