Strange centering

Question

\centering command, that I use in my document gives strange output - values aren't centered equally

image below should let you understand (elements in red frame and two not framed "value" strings in table, are not centered) code for this page/document:

\documentclass[twoside,titlepage]{article}
\usepackage[polish]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[a4paper,inner=3.5cm,outer=2.0cm,top=2.0cm,bottom=2.0cm]{geometry}
\usepackage{multicol}
\usepackage[titletoc,title]{appendix}
\usepackage[table]{xcolor}
\usepackage{multirow}
\usepackage{mathtools}
\newcommand{\appendixtitle}[2]{\begin{center}(#1)\\ ~ \\ {\Large #2}\end{center}}
\newcolumntype{z}[1]{%
    >{\centering\hspace{0pt}}m{#1}}%
\newcommand{\tnl}{\tabularnewline}
\usepackage{lipsum}
\begin{document}
    \begin{appendices}
        \section[~]{\centering}
        \appendixtitle{type}{appendix title}
        \newlength{\celllen}
        \setlength{\celllen}{\textwidth/5}
        \lipsum[1]
        \begin{table}[!htb]
            \caption{multirowed}
            \centering
            \begin{tabular}{|*{4}{z{\celllen}|}}
                \hline
                \multirow{2}{\celllen}{\centering
                    very very very long cell \newline symbol \newline unit
                } & \multicolumn{3}{c|}{ \textbf{   Description } } \tnl
                & value & value & value \tnl \hline
            \end{tabular}
        \end{table}

        \begin{table}[!htb]
            \caption{final}
            \centering
            \begin{tabular}{|*{4}{z{\celllen}|}}
                \hline
                \multirow{5}{\celllen}{\centering
                    very very very long cell \newline symbol \newline unit
                } & \multicolumn{3}{c|}{ \textbf{   Description } } \tnl
                & value & value & value \tnl \cline{2-4}
                & \multicolumn{3}{c|}{ \textbf{ Description }, symbol, unit } \tnl
                & value & value & value \tnl \cline{2-4}
                & \multicolumn{3}{c|}{ \textbf{ Description }, symbol, unit } \tnl \hline
                value \newline (comment) & value & value & value \tnl \hline
                value \newline (comment) & value & value & value \tnl \hline
            \end{tabular}
        \end{table}
    \end{appendices}
\end{document}

How can I make all those red-framed-texts (and "value" strings I forgot to frame) centered, just like other strings

P.S. help with first table (text overflow) is greatly appreciated ;)

Answer 1

Don't use \newline but \\.

\documentclass{article}
\begin{document}
\centering

aaa\\ bbbbbb\\ cccccc

aaa\newline bbbbbb\newline cccccc

\end{document}

And try to make simpler examples. Wading through all this \multirow etc doesn't make it easy to debug your code.

Answer 2

the mechanism for \newline makes this command be equivalent to \\, so what precedes it is treated as an ordinary "paragraph" (ending with \parfillskip glue, messing up the centering). (you are using this inside a table, which means you shouldn't use \\ directly.)

change \newline to \break, avoiding all fancy additions (but also all checking), and every line will center as desired.