Concept

Asymptotics — where it appears

How a quantity behaves in the limit of a control parameter, as against how it behaves over the range actually measured. The two differ wherever a law is only asymptotically a power law, so an exponent fitted over a short sweep is a property of the sweep as much as of the law.

Named by 7 essays across 5 fields — each of them below, with the objects they name alongside it.

-2024-0.500-0.25000.2500.500where the viewer sits, as a fraction of the sitting distance (log₁₀)the two eyes' vertical disagreement, in arcminutes (log₁₀)15′ fusion limitthe raw differencewhat a common frame leavesthe sitting distancecurved monitor, against the chairlimit at 29 cm

The distance at which the eyes part

The two eyes' disagreement on a curved screen was measured at each screen's own sitting distance and reported as a null result. The sitting distance is a parameter and the chair moves — swept, the raw difference falls like the cube of it and the residual like the fourth power, and a viewer twenty-nine centimetres from a curved monitor crosses the fusion limit the null result was quoted against.

screen · Stereodisplay
0102030401234the marking error, in pixelsthe error of the answer, in per centupper curve: the closure wrong · lower: the closure exactfloor 6.0%

The floor a better camera cannot reach

Sweep the marking error from four pixels down to a hundredth and the measurement's error falls thirty-fold and then stops — at 6.0 per cent, which is exactly the six per cent the reference's assumed shape was wrong by. With the closure exact the same sweep keeps falling to 0.06 per cent. The crossing is at half a pixel, and it can be computed before the photograph is taken, which makes it a decision about equipment rather than a discovery about it.

metrology · Uncertainty
-4-3-2-1000.50011.502how much more effort, log₁₀ of the controlhow much of the error is left, log₁₀ of the first samplepanorama-seam · −0.92panorama-vertical · floorsilhouette-hull · −2.00silhouette-notch · flooranamorph-sagitta · −2.30anamorph-sagitta-intervals · −2.00mirrorball-size · −1.007 laws, 12 samples each2 with a floor · 5 without

An error with two terms

Two results from machineries with nothing in common have now found the same shape. A panorama's parallax separates into a term that halves every time the frame count doubles and a term with no frame count in it at all; a silhouette's error into an excess that falls as one over the square of the view count and the area of a concavity that is the same number at four views and at a hundred and twenty-eight. Fitting both terms turns the distinction into a measurement, and pointed at seven of this collection's own laws it reads every one of them the way its own essay does.

foundations · Buyable
0.4000.6000.80011.201.40braccia in the pavement (log₁₀)the worst departure of a mark, in pixels (log₁₀)steppedmeasured from the zerothe same hand, laid off two ways√n against n^0.21

Stepped, or measured from the zero

The same hand at the same precision, laying the same braccia off two ways — dividers walked from the last mark accumulate and grow as the square root of the count, while marks set from a common origin do not accumulate at all. The difference is not which method was used — it is where the zero is, and only the second is recorded in the drawing.

construction · Handerror
05101520123how many decades of the control were sweptlargest floor the data cannot rule out (% of the first sample)everything in here is still possiblea floor-free law at 1% noise21.5% at 0.3 decades · 0.00% at 3

What a null result is worth in decades

The first draft of this expected a short sweep to invent a floor, on the reasoning that least squares always spends a free parameter. It does not — on exact data the fitted floor of a floor-free law comes back at three parts in a quadrillion. The failure is the other one and it is worse because it looks like a result. Over a third of a decade at one per cent noise, floors of a fifth of the first sample are still consistent with the data, and the fit reports none while telling the truth.

foundations · Buyable
-1.50-1-0.50000.50011.5022.50how far back the eye stands, in object radii (log₁₀)how far a mark lands from where the direction puts it, in metres (log₁₀)one design samplethe faces settlethe marks settlea seating rake, from a point and from a direction3 radii against 34

Two distances to infinity

A parallel projection is the limit of a perspective one, and the limit arrives twice. Which faces get painted settles within three object radii, because a face is either round the back or it is not; where each mark lands falls like one over the distance and is still out at thirty-four. Far enough away has two answers an order of magnitude apart.

parallel · Limit
-1.50-1-0.50000.50011.5022.50how far back the eye stands, in object radii (log₁₀)how far a mark lands from where the direction puts it, in metres (log₁₀)one design samplethe faces settlethe marks settlea seating rake, from a point and from a direction3 radii against 34

Two distances to infinity

A parallel projection is the limit of a perspective one, and the limit arrives twice. Which faces get painted settles within three object radii, because a face is either round the back or it is not; where each mark lands falls like one over the distance and is still out at thirty-four. Far enough away has two answers an order of magnitude apart.

parallel · Limit

Named alongside it

The objects these essays reach for when they reach for this one.

Power lawSamplingToleranceError terminstrument limitResidualcentre of projectionConditioningDemonstrationIdentifiabilityModel errorOcclusion

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