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\documentclass[a4paper]{scrartcl}
\begin{document}
~
\end{document}
和
\documentclass[letterpaper]{scrartcl}
\begin{document}
~
\end{document}
（注意：标准类别的结果相同，即
\documentclass[a4paper/letterpaper]{article}
\usepackage{typearea}
），我得到
Package: typearea 2022/10/12 v3.38 KOMA-Script package (type area) \ta@bcor=\skip48 \ta@div=\count185 Package typearea Info: You've used standard option `a4paper'. (typearea) This is correct! (typearea) Internally I'm using `paper=a4'. (typearea) If you'd like to set the option with \KOMAoptions, (typearea) you'd have to use `paper=a4' there (typearea) instead of `a4paper', too. \ta@hblk=\skip49 \ta@vblk=\skip50 \ta@temp=\skip51 \footheight=\skip52 Package typearea Info: These are the values describing the layout: (typearea) DIV = 10 (typearea) BCOR = 0.0pt (typearea) \paperwidth = 597.50793pt (typearea) \textwidth = 418.25555pt (typearea) DIV departure = -6% (typearea) \evensidemargin = 17.3562pt (typearea) \oddsidemargin = 17.3562pt (typearea) \paperheight = 845.04694pt (typearea) \textheight = 595.80026pt (typearea) \topmargin = -25.16531pt (typearea) \headheight = 17.0pt (typearea) \headsep = 20.40001pt (typearea) \topskip = 11.0pt (typearea) \footskip = 47.6pt (typearea) \baselineskip = 13.6pt
和
Package: typearea 2022/10/12 v3.38 KOMA-Script package (type area) \ta@bcor=\skip48 \ta@div=\count185 Package typearea Info: You've used standard option `letterpaper'. (typearea) This is correct! (typearea) Internally I'm using `paper=letter'. (typearea) If you'd like to set the option with \KOMAoptions, (typearea) you'd have to use `paper=letter' there (typearea) instead of `letterpaper', too. \ta@hblk=\skip49 \ta@vblk=\skip50 \ta@temp=\skip51 \footheight=\skip52 Package typearea Info: With paper sizes other than (almost) `A4' predefined (typearea) DIV values do not exist. Using DIV calculation for good (typearea) line width (unless using `version=3.24` or prior). DIV calculation for typearea with good linewidth. Package typearea Info: These are the values describing the layout: (typearea) DIV = 7 (typearea) BCOR = 0.0pt (typearea) \paperwidth = 614.295pt (typearea) \textwidth = 351.02573pt (typearea) DIV departure = 3% (typearea) \evensidemargin = 59.36464pt (typearea) \oddsidemargin = 59.36464pt (typearea) \paperheight = 794.96999pt (typearea) \textheight = 459.8002pt (typearea) \topmargin = 3.89714pt (typearea) \headheight = 17.0pt (typearea) \headsep = 20.40001pt (typearea) \topskip = 11.0pt (typearea) \footskip = 47.6pt (typearea) \baselineskip = 13.6pt
换句话说，信纸的默认文本宽度和高度比 A4 的要小得多（DIV=7相比之下DIV=10，\textwidth信纸为 351pt，A4 为 418pt）。线条宽度的差异非常大 – A4 版本的线条比信纸长 19% 以上！
我想知道为什么不同纸张尺寸的默认值会有如此大的差异。据我所知，存在一定的“最佳”行长，因此无论纸张尺寸如何，我都希望 typearea 始终保持\textwidth相同。事实上，信纸的边距对我来说看起来太宽了。
现在，使用不同的程序确定值的事实可能与此有关：如 KOMA-Script 文档（表 2.2）中所述，DIVA4 纸有硬编码的默认值（DIV=10默认字体大小），而对于信纸，我们可以看到该DIV值是根据某种算法自动计算的（“包 typearea 信息：对于除（几乎）`A4' 以外的纸张尺寸，不存在预定义的 DIV 值。使用 DIV 计算以获得良好的线宽（除非使用version=3.24或先前）。”。事实上，使用DIV=calc得到的a4paper结果DIV是 8，而不是 10！然而，这并没有回答为什么结果如此不同。据推测，如果预定义值和自动计算都给出了良好的印刷效果，那么得到的线宽应该（大约）匹配！
答案1
我认为该typearea包从未考虑过信纸。这确实是给出的信息的内容（不存在预定义的 DIV 值）。为什么选择 7 超出了我的想象。
但你可以指定选项DIV=10
\documentclass[
paper=letter,
DIV=10,
]{scrartcl}
\begin{document}
x
\end{document}
并得到
Package typearea Info: These are the values describing the layout:
(typearea) DIV = 10
(typearea) BCOR = 0.0pt
(typearea) \paperwidth = 614.295pt
(typearea) \textwidth = 430.00653pt
(typearea) DIV departure = -9%
(typearea) \evensidemargin = 19.87424pt
(typearea) \oddsidemargin = 19.87424pt
(typearea) \paperheight = 794.96999pt
(typearea) \textheight = 568.60025pt
(typearea) \topmargin = -30.173pt
(typearea) \headheight = 17.0pt
(typearea) \headsep = 20.40001pt
(typearea) \topskip = 11.0pt
(typearea) \footskip = 47.6pt
(typearea) \baselineskip = 13.6pt
(typearea) on input line 1767.