Accuracy and Precision

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Accuracy and Precision

Kettrick was uncomfortable, but he would never show it. Being called to a meeting with your employer was always cause for anxiety, but it was especially so in certain lines of work where lives hung in the balance.

One of many men with guns nodded towards the unassuming door in the grand kitchen of the mansion, and Kettrick opened it and walked through a small rear lobby before going outside. There was a paved path which snaked its way across a manicured lawn, the grass a faded tone in the evening light. Ahead of him lay an extensive wooden building, made in a simple design, with barn-style double doors.

The workshop, he thought.

His employer ran a vast, secretive, and wholly illegal enterprise, but did so via an array of intermediates and enforcers. It was rare indeed to see the man himself, and part of the reason for that was how much of his time he spent hidden away in this place.

The leftmost of the barn doors was ajar, with another armed guard standing alongside, but Kettrick earned barely a glance as he passed by and went into the brightly lit chamber beyond. He looked around, fascinated despite himself, and his step faltered for a moment at the scale of it all.

The walls were encrusted with every manner of tools and organisers and devices, many of which Kettrick had never seen before. Some seemed to be for woodworking, some for electronics and electrical uses, and there were also a great many whose purpose he couldn’t begin to guess.

There was a lumber storage facility in one distant corner, and almost half of one wall was devoted to an elaborate array of sorters and caddies for every kind of fastener and component. Power tools were racked by type, and still more tools were built into a variety of benches and work-surfaces which lined the perimeter and also occupied much of the central floor space.

Above his head, Kettrick saw a suspended gantry which routed cables and conduits in all directions, and also bore light fixtures which were dazzling in their cold harshness. Some of the infrastructure above was clearly for power, and some for ventilation, and there was also what he assumed to be an extensive dust-collection system, whose many nozzles reached down like tentacles towards the larger saws and other cutting machines. The whole place smelled splendidly of sawdust and lubricants, and there were many projects in various stages of completion dotted around.

Belatedly, Kettrick spotted the man he’d been brought here to see. He had never known his name, always hearing him referred to as any of the various terms for boss or similar, and Kettrick felt the discomfort rise up in him once again as he reluctantly began to move forwards through the maze of hardware.

The other man was facing mostly away from him, at a workbench almost all the way up the right-hand side of the building, head down and focused on something. There was an ambient rumble of air conditioning, but no other machinery was currently in operation. Kettrick reached the vicinity of the workbench, but he stopped short and stood awkwardly for what felt like several minutes, but which was probably only thirty seconds or so. Just as he was considering announcing himself, the older man spoke without turning around or even looking up.

“Do you know what this is?” he said, holding up a short metal device which was simultaneously reminiscent of a spanner, a surgical implement, and some sort of ruler. Kettrick looked at it, and found that his memory did indeed have an answer.

“A calliper,” he replied, and the other man nodded.

Kettrick saw that there were a multitude of metal bars and blocks on the workbench, each one anodised in a vivid red colour, and each bearing markings. They were beautiful, in their own way, and they looked like they had been manufactured to a high standard. There was nothing else on the bench, and it didn’t seem like the man had been building or repairing anything.

“And these?” the other man asked, and Kettrick had to hide the fact that the new enquiry had startled him a little.

He leaned forward to read some of the markings on the pieces of metal, seeing that they had been engraved by a laser rather than painted onto the surface. Each one was a numerical value in millimetres, and it was immediately apparent that those values indicated the thickness of the respective object. Kettrick frowned.

“They are gauge blocks,” the other man said, quietly and evenly, as if teaching a student. “They allow for comparison against known dimensions, for reference. They help avoid measurement.”

Kettrick nodded slowly, unsure why he was being told this. His mind flashed to the many saws and other machines, and their own worktables, which surrounded him. He could understand why the blocks would be useful, when he thought about it.

“Because measurement introduces error,” Kettrick replied, plucking the phrase from some obscure recollection of a class at high school, so many years ago. Had it been physics? Or perhaps woodwork? The details were elusive.

The older man straightened now, and turned to face him, still holding the sleek and somehow cruel-looking calliper.

“And so we come to the crux of the matter,” he said.

For an instant, Kettrick was absolutely certain that he was about to be stabbed between the ribs with the tool, but the moment passed as the older man looked at him appraisingly for several seconds. Then he spoke again.

“Error is an inevitable and inseparable component of any measurement,” the man said. “Or of any system. These gauge blocks are manufactured to strict tolerances, and those tolerances are margins of error. Beyond those margins, their true dimensions are unknown — if not unknowable.”

He held the calliper up now, looking at it the same way that a less monstrous man might look at his own child’s face.

“This device produces measurements down to intervals of 0.01 millimetres, but those measurements can only be trusted to within 0.03 millimetres. Do you know the proper names for the distinction?”

Kettrick shook his head, truthfully. He was interested now, despite the situation, and despite the obvious danger he was in. The man nodded, as if to acknowledge the honesty of his response. He continued.

“They are called accuracy and precision,” he said. “This device’s precision — the minimum interval between its measurements — is 0.01mm. But its accuracy is only 0.03mm. It is accuracy, not precision, which asserts how close a measurement is to the true value of the thing being measured.”

The man opened the calliper, its gleaming steel jaws sliding smoothly apart. Other components moved in tandem with the primary jaws, including a probe extending from the end of the ruled length of the device, and two smaller and inwards-facing prongs on the upper surface crossed in front of each other in opposition. It made a soft, papery sound, and Kettrick believed absolutely that it could measure down to such tiny fractions of distance, without any electronics or power supply.

“You allowed the woman to live, in direct contradiction of your instructions,” the older man said, and now Kettrick’s heart dropped.

A moment’s indiscretion on his part, giving in to phantom pity. The target resembled his deceased sister just a little too much. That was all it had taken. The woman had sworn to disappear, just as if she really had been executed that day. He saw little point in denying it.

“You’re right,” he replied, his voice calm and resigned. “I did. And I lied about it.”

The older man held the open calliper up in front of his own face, allowing himself to look upon Kettrick through the frame of its sharp and perfectly parallel jaws.

“I employ you because I have no doubts about your precision, Mr. Kettrick,” the man said, before lowering the callipers and turning away once more to focus on the workbench.

He made a gesture of dismissal, and Kettrick realised that he was actually getting away with a warning. He half-bowed before he could stop himself, and felt embarrassed even though his movement had gone unseen. He withdrew silently and quickly, heading for the door. The older man’s voice came drifting from behind him just as he reached it.

“Never again make me doubt your accuracy.”

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