user27766: I was reading Modern Chess Openings by Nick de Firmian, and found "columns 1-24 deals with 2...exf4 " in relation to a theory table. So what does "columns 1-24" mean?

user1751: This table can be thought of as a tabular representation of an opening tree of in-theory moves where the rows (y-axis) represent the flow of the game and the columns (x-axis) refer to variations/branches in the tree that can occur.
The author in your quote indicated that 2...exf4 spans a family 24 variations/sub-variations that are noteworthy (and considered theory) for reference.
Here's an example for another such page on these NCO/MCO opening references.

If this is confusing,  let's consider a simpler example with the first few moves (with some early deviations) from the popular Danish Gambit.
Here's what a fragment of the opening tree would look like.

If I wanted to represent/transform this tree into a table, it would look like this.


27766: <p>I was reading <em>Modern Chess Openings</em> by Nick de Firmian, and found &quot;columns 1-24 deals with 2...exf4 &quot; in relation to a theory table. So what does &quot;columns 1-24&quot; mean?</p>
 1751: <p>This table can be thought of as a tabular representation of an opening tree of in-theory moves where the rows (y-axis) represent the flow of the game and the columns (x-axis) refer to variations/branches in the tree that can occur.</p>
<p>The author in your quote indicated that 2...exf4 spans a family 24 variations/sub-variations that are noteworthy (and considered theory) for reference.</p>
<p>Here's an example for another such page on these NCO/MCO opening references.</p>
<p><a href="https://i.stack.imgur.com/1uzzF.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1uzzF.png" alt="enter image description here" /></a></p>
<p>If this is confusing,  let's consider a simpler example with the first few moves (with some early deviations) from the popular <a href="https://en.wikipedia.org/wiki/Danish_Gambit" rel="nofollow noreferrer">Danish Gambit.</a></p>
<p>Here's what a fragment of the opening tree would look like.</p>
<p><a href="https://i.stack.imgur.com/91wPr.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/91wPr.png" alt="enter image description here" /></a></p>
<p>If I wanted to represent/transform this tree into a table, it would look like this.</p>
<p><a href="https://i.stack.imgur.com/40spb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/40spb.png" alt="enter image description here" /></a></p>
