# Why chapter label below the section label on new page even if by setting same spacing before title (use titlesec package)?

\documentclass{book}
\usepackage[margin=0pt,papersize={50pt,70pt}]{geometry}
\usepackage{titlesec}
\titleformat{\chapter}{\Huge\bfseries}{}{0em}{}
\titleformat{\section}{\Huge\bfseries}{}{0em}{}
\titlespacing*{\chapter}{0pt}{0pt}{0pt}
\titlespacing*{\section}{0pt}{0pt}{0pt}
\begin{document}
\chapter{abc}
\newpage\section{abc}
\end{document}


This question is concerned with Writing several lines before chapter title

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There should be a reason why

\titlespacing*{\chapter}{0pt}{-19pt}{0pt}


works as you'd like. It must be in the internals of titlesec.

The amount of backspacing must be -17.5pt if \huge is requested, -16.6pt with \LARGE. With \Huge the baselineskip is 30pt, with \huge it's 25pt and with \LARGE it's 22pt.

The sizes are actually obtained as

-(\topskip+\baselineskip-\ht\strutbox)

where the \strut is computed in the font size. For example, with \Huge the height of a strut is 21pt, so the computation is

-(10pt + 30pt - 21pt) = -19pt

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thanks your explanation. But, why the section label doesn't need backspacing adjustment? –  dearmath May 19 '11 at 17:16
@dearmath: It's the chapter heading that skips down and backspacing of the right amount places it in line with the section label in the following place. –  egreg May 19 '11 at 17:18
Thanks! –  dearmath May 20 '11 at 3:00