My in-laws live a mile from me in Falls Church, and we both get The Post. They give me their coupon sections from the Sunday paper. Usually the coupon sections are the same, but not always. Is that intentional or accidental?

Stephen Donnelly, Falls Church

Let us travel to The Post's printing plant in Springfield, where four complex machines, the biggest of them as long as a football field, are assembling the assortment of inserts that will be bagged in plastic and put into the Sunday paper.

The bagged items are known as preprints. The contents of each bag are the result of a precise recipe.

How precise? Pretty darn precise, said Vance Dippold, The Post's advertising preprint manager. The Post calibrates, or "zones," its preprint advertising down to the Zip code level, allowing businesses to choose exactly where they want their materials to go.

Advertisers have various reasons for picking and choosing who gets what. "One could be how far away [readers] are from the retail location," said Vance. "Some retailers will want to go within a five-mile radius of a store. . . . Other retailers will look at the shopping pattern of customers. Ever been in a store where they ask for your Zip code while they're ringing you up?"

A merchant might want a particular demographic, such as a Zip code heavy on families with children or people who own their homes.

Vance said preprint advertisers can go into 225 zones. On a typical autumn Sunday, 150 unique advertising pieces are divvied up in different ways. In the course of a year, about 2 billion preprinted pieces are inserted in the paper.

Things might get even more granular in the future. "We are in the process of working towards dividing the Zip codes up into pieces," Vance said.

What are those little numbers at the top of the front page of The Washington Post, above that gray bar?

There are all sorts of numbers and letters up there. A cabalist could spend weeks trying to discern their meaning. Or he could just read this column.

Starting on the left, there's the year (we're in our 128th) and the number (counting from Dec. 6, which is when we printed our first issue, in 1877). Then there's either an R, an S, an M1 or an M2.

R stands for Regional, the edition that we start printing around 11:15 p.m. It's delivered to about 70,000 people in counties outside the Washington region. S stands for Suburban. Printing starts about 12:15 a.m. It's our biggest edition, going to roughly 450,000 readers in the burbs and parts of the District. Then there are two Metro editions: M1 and M2.

"M1 is only an occasional edition, when we have late-breaking sports or news that didn't happen in time to make it in the Suburban but we want to get in fast," said Vince Bzdek, a deputy assistant managing editor.

M2 is the final edition, printed about 2 a.m. Its 150,000 copies go to the District, and most are sold in street boxes.

Just as the ads are zoned, so are the articles, with some stories given more or less prominence depending on where that paper is delivered. The MD, VA or DC to the right of the edition info indicates the editorial zone. (On Saturdays and Mondays, the paper is zoned in two ways: Virginia [VA] or DC/MD, although the editorial content is nearly always the same.)

To the right of the date is something starting with either M or V. That indicates where that paper was printed: in College Park or Springfield. A number tells us which of the four presses at each location printed the paper: i.e., M2, V4.

Sometimes at the top of a page you'll see a K. That means there was a mistake on an earlier version of the page and it had to be "killed," our wonderfully violent word for correcting the error.

We have for years used a gadget to start charcoal for our grill. You put two or three sheets of newspaper in the bottom of a metal tube and charcoal in the top. You light the newspaper, and in about 15 minutes you have glowing coals. This year we have been having trouble getting the newspaper to light properly. Did Washington Post newsprint change recently?

Peter D. Johnson, Silver Spring

Answer Man forwarded this inquiry to Lionel Neptune, the Post executive responsible for what might be the single most important part of the paper: the paper itself.

Lionel said that there has been no significant change in the formulation of the paper The Post is printed on. But Lionel pointed out that there is no one single source of paper for The Post. He buys it from all over, and there are several ways that one batch could differ from another: The newsprint could be composed of different types of fiber (that is, the wood could come from different sorts of trees); it could be pulped in different ways; and it could vary as to the amount of recycled product used in its manufacture.

"While I can't point to any specific research to support this, it seems reasonable to assume that the combustible characteristics of newsprint would vary based on the particular combination of these variables used to produce the paper," said Lionel. Given that The Post receives newsprint from multiple paper companies -- and from several mills and machines within those companies -- it is possible that the papers could burn in different ways.

Answer Man has a thought: Perhaps The Post should be published on special mesquite newsprint, for a lovely smoky flavor.

Questions? Write Or 1150 15th St. NW, Washington, D.C. 20071.