KOMA-Script: Why does "DIV=calc" destroy the initial geometry?

Question

Why does the DIV=calc-command modify the whole layout geometry, even if the binding correction BCOR is set to 0mm?

Let's have a look at two simple examples to explain my question.

---

1. Example

In the first example, I completely disactivate the BCOR and the DIV=calc commands by commenting them out. The result will be a harmonious looking layout with nice borders.

---

Minimum Working Example (MWE):

\documentclass[twoside=false]{scrbook}

\usepackage{blindtext}

% \KOMAoptions{BCOR=0mm}
% \KOMAoptions{DIV=calc}

\begin{document}
    \blinddocument
\end{document}

---

Screenshot of the result:

---

2. Example

However, if I switch on the DIV=calc-command even with BCOR=0mm, the whole layout is getting changed. The result will be a strongly modified geometry with (in my eyes) too wide and inharmonious border widths.

---

Minimum Working Example (MWE):

\documentclass[twoside=false]{scrbook}

\usepackage{blindtext}

\KOMAoptions{BCOR=0mm}
\KOMAoptions{DIV=calc}

\begin{document}
    \blinddocument
\end{document}

---

Screenshot of the result:

---

What is the reason for this behavior?

Why does the whole layout change, even with 0mm in BCOR? I think the initial layout without DIV=calc is looking way more natural, doesn't it?

Answer 1

If you do not set option DIV as class option package typearea is loaded using DIV=default. That means: either there exists a default value (only for a4 paper and the fontsizes 10pt, 11pt or 12pt) or DIV=calc is used automatically.

Your example does not set paper, fontsize or DIV, so the defaults paper=a4, fontsize=11pt, DIV=default are used. This results in the preset value DIV=10.

With DIV=calc package typearea recalculates the DIV value depending on the current font to get a recommended number of characters per line. In your example this is DIV=8. You can find this value in the log file.

If you do not want a change of DIV while the page layout is recalculated, do not use DIV=calc. Replace it by DIV=current (current value of DIV) or DIV=last (last argument of option DIV - this could be a number or a symbolic value like default).

But if you change BCOR in the preamble the recalculation of the page layout is already done using DIV=last. In your example this would be DIV=default resulting in DIV=10. So there is no need to set DIV again. See also DIV and BCOR setting in KOMA (best practices).

Note that \recalctypearea recalculates the page layout using options BCOR=current and DIV=last.

If the margins should be smaller set a larger DIV value i.e. DIV=12.

If you need special margins you could set KOMA-Script option usegeometry and load package geometry to change the margins.

Answer 2

TL;DR: DIV=calc is supposed to alter layout as it is an option for page layout construction.

Just my opinion on the last question: No, it doesn't look more natural without DIV=calc. At least if you are used to this setting.

But to clarify what the purpose of both settings is (more or less to be read in the KOMA documentation):

• BCOR sets a binding correction, which is a horizontal shift of the text block away from the inner margin.
• DIV now uses the remaining page (without binding correction) to divide the page into equally high parts. It does the same on the horizontal axis (equally wide parts). The top margin is the uppermost stripe, the bottom margin the two bottom-most stripes. It does the same with the inner-most stripe (like top) and the two outer-most stripes (like bottom).

So there are some predefined divisions of the page (DIV ranging from 6 to 15 [stripes per page]). DIV=calc is now supposed to choose the most aesthetic page layout automatically. As soon as you do \recalctypearea (or alter one of the aforementioned KOMA options) it will try to reduce the line width so that not too many characters will make up a line (tradition in typography, there are values like 66 characters per line as a rule of thumb).

There are other methods for automatic calculation like DIV=classic, but you seemingly do not want to do this.

Now to your question: As I've just explained, DIV is supposed to change page layout. Hence setting it will result in different margins and a drastically altered visual appearance, which aims at helping the reader focus, because on paper shorter lines are better to read than lines of 80-100 characters.