What the lookup knows, and what it only estimates

What it will not do, stated first

The house style here is to say no before saying yes, with reasons rather than adjectives. Applied to the box:

::lines It will not price a trip | Every figure on this site is per person for the ground and starts the moment you land. Nothing the box returns is part of one. // It will not tell you a schedule | It has no timetable, no routing and no connection data, and none is available to it. // It will not recommend anything | It ranks nothing, compares nothing and holds no view on which airport is better. // It will not remember you | It takes no name, keeps nothing between visits and has nowhere to put either. // It will not sell you a seat | The far end does that, on its own pages, under its own conditions.

That is five refusals before a single feature. What remains is worth the space it takes, but only just, and only because the alternative is a reader guessing at the one number this office does not print.

Whose desk it lands on

Not this one. The button hands the question to a booking company, a separate firm reached over a subdomain this site lends it. Producing the figure, reserving the seat, accepting the card and writing the ticket all happen over there, under a rulebook this site had no hand in. Should you buy, a slice of a margin fixed long before your visit returns here from their end.

What it knows exactly

::lines The two airport codes | Three letters each, taken from the list and never typed free // The two dates | Exactly as you set them // The cabin and the seat count | Exactly as you set them

These are the things you told it. They travel unchanged and nothing is added to them.

What it only estimates

One number, and it is labelled where it appears:

::lines How it is worked | The shortest path over the globe between two stored positions, at a flat 500 miles an hour, with forty minutes added for climb, approach and taxi, and so worked from geometry rather than from a timetable // Accuracy of the positions | About five kilometers, which is far below anything that would move the answer // What is left out | Wind, routing, the connection, the aircraft, and the two hours on the ground before any of it

Fly nonstop and the figure will sit close. Route through a connecting airport and it will not, and the box cannot tell in advance which you will be offered. A number of that kind belongs in a sentence that admits what it is, which is why the line on the front page says so rather than printing a bare figure.

A feature that was built and then thrown away

Each of the twenty-five trip pages names the airport it is reached through. It would have been neat for the box to notice that your destination is one of them and point you at the page.

It was built. Matching the airports named on those pages produced twenty-one matches, and two of them were on the wrong continent: the three letter code for Flores in Guatemala is not the Flores in Indonesia, and the code for Merida in Mexico is not the Merida in Spain. A reader flying to Central America would have been shown a trip through the Yucatan or the Balkans and told this desk reserves it.

The specification for this site opens by saying nothing on it is invented. A guess wearing the clothes of a fact is exactly what that sentence forbids, so the feature was removed rather than patched. This paragraph is what stands where it would have gone.

The eighteen characters it does send

St Louis to Lisbon, out on the fourth of May, home on the fourteenth, economy, two seats:

STL0405LIS1405200

::lines First three | The airport it leaves // Next four | The outbound date, day then month // Next three | The airport it reaches // Next four | The return, written the same way // Then one, or none | Which cabin. An empty slot means economy; otherwise w, c or f for premium economy, business or first // Last three | Adults holding a seat, children of two to eleven, infants riding on a lap

Seventeen for that example because economy takes no letter, eighteen at the longest, thirteen for a single leg. Nothing about a person fits in a string of that shape.

What stays on your side

::lines Your name | There is no field // Any way to reach you | None // A card | This site owns no field capable of taking those digits // What you wrote to the desk on another page | Reaches this office alone and is invisible to the box // The distance it worked out | Calculated in front of you and sent nowhere

One download of the airport list happens the moment you begin typing, and after that the network goes quiet until you press the button.

Seven refusals, each beside its own field

Before the script arrives the button is disabled and looks it. A string the far end cannot read comes back as a blank page, which says less than a plain no.

An airport typed out but never taken from the list. Both ends the same. A departure already behind us. A return dated before the departure, which the field settles by emptying itself as soon as the departure passes it. A tenth passenger in a seat. A lap infant with no adult booked beside them. And any date more than eleven months out.

The eleven month horizon, and what draws it

Each date in that string gets four characters: a day, a month, and no year at all.

Inside a year only one May can be meant. Past that the string stops being read and starts being assumed: ask about a date fifteen months out and the near May is what gets used, live figures arrive against it, and the substitution is announced nowhere. Eleven months is the last point where four characters have one meaning.