How to fix sizes between different fonts

Question

actual problem:

How to make a second font the same "actual" size of the first one.

\documentclass[a4paper, 12pt]{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage[ngerman]{babel}
\usepackage{amsmath}

\newcommand*{\afont}{\fontsize{14}{48}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\texta}{\afont}
\newcommand*{\bfont}{\fontsize{21}{48}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\textb}{\bfont}
\newcommand*{\cfont}{\fontsize{30}{48}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\textc}{\cfont}

\newcommand{\printa}[1]{\texta{#1}}
\newcommand{\printb}[1]{\textb{#1}}
\newcommand{\printc}[1]{\textc{#1}}

\DeclareMathOperator{\matha}{\printa{SPEZIAL}}
\DeclareMathOperator{\mathb}{\printb{SPEZIAL}}
\DeclareMathOperator{\mathc}{\printc{SPEZIAL}}
\DeclareMathOperator{\mathd}{\printd{SPEZIAL}}

\begin{document}
\chapter{Test}
This Is A Great Sentence With A $\matha$ Word.\\
{\Large This Is A Great Sentence With A $\mathb$ Word.}\\
{\Huge This Is A Great Sentence With A $\mathc$ Word.}\\
\\
SPEZIAL=14 rest=12 difference=2\\
SPEZIAL=21 rest=17 difference=4\\
SPEZIAL=30 rest=25 difference=5
\end{document}

Is there a way to define normalsize, large, Large, ... of the second font to fit to the rest of the text?

---

I'm using two different fonts in one document.

Short form:

\documentclass[a4paper, 12pt]{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage[ngerman]{babel}
\usepackage{amsmath}

\newcommand*{\myfont}{\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\textmy}{\myfont}

\newcommand{\printmy}[1]{\textmy{#1}}

\DeclareMathOperator{\mathmy}{\printmy{SPEZIAL}}

\begin{document}
\chapter{Test}
This Is A Great Sentence With A $\mathmy$ Word.\\
This Is A Great Sentence With A {\large $\mathmy$} Word.\\ %bad fix
{\large This Is A Great Sentence With A $\mathmy$ Word.}
\end{document}

The SPEZIAL word doesn't use the right size.

---

Long form:

Here a (not really) MWE, but a test document with different sizes.

\documentclass[a4paper, 12pt]{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage[ngerman]{babel}
\usepackage{amsmath}

\newcommand*{\nofont}{\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\textno}{\nofont}
\newcommand*{\largefont}{\large\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\textlarge}{\largefont}
\newcommand*{\afont}{\fontsize{12}{90}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\texta}{\afont}
\newcommand*{\bfont}{\fontsize{12}{1}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\textb}{\bfont}
\newcommand*{\cfont}{\fontsize{12}{200}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\textc}{\cfont}
\newcommand*{\dfont}{\fontsize{12}{48}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\textd}{\dfont}
\newcommand*{\efont}{\fontsize{13}{48}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\texte}{\efont}
\newcommand*{\ffont}{\fontsize{14}{48}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\textf}{\ffont}
\newcommand*{\gfont}{\fontsize{15}{48}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\textg}{\gfont}
\newcommand*{\hfont}{\fontsize{16}{48}\itshape\fontfamily{qzc}\selectfont}
\DeclareTextFontCommand{\texth}{\hfont}

\newcommand{\printno}[1]{\textno{#1}}
\newcommand{\printlarge}[1]{\textlarge{#1}}
\newcommand{\printa}[1]{\texta{#1}}
\newcommand{\printb}[1]{\textb{#1}}
\newcommand{\printc}[1]{\textc{#1}}
\newcommand{\printd}[1]{\textd{#1}}
\newcommand{\printe}[1]{\texte{#1}}
\newcommand{\printf}[1]{\textf{#1}}
\newcommand{\printg}[1]{\textg{#1}}
\newcommand{\printh}[1]{\texth{#1}}

\DeclareMathOperator{\mathno}{\printno{SPEZIAL}}
\DeclareMathOperator{\mathlarge}{\printlarge{SPEZIAL}}
\DeclareMathOperator{\matha}{\printa{SPEZIAL}}
\DeclareMathOperator{\mathb}{\printb{SPEZIAL}}
\DeclareMathOperator{\mathc}{\printc{SPEZIAL}}
\DeclareMathOperator{\mathd}{\printd{SPEZIAL}}
\DeclareMathOperator{\mathe}{\printe{SPEZIAL}}
\DeclareMathOperator{\mathf}{\printf{SPEZIAL}}
\DeclareMathOperator{\mathg}{\printg{SPEZIAL}}
\DeclareMathOperator{\mathh}{\printh{SPEZIAL}}

\begin{document}
\chapter{Test}
This Is A Great Sentence With A $\mathno$ Word.

This Is A Great Sentence With A $\mathlarge$ Word. I guess this is the right size.

{\large This Is A Great Sentence With A $\mathlarge$ Word. Doesn't grow.}

This Is A Great Sentence With A $\matha$ Word.

This Is A Great Sentence With A $\mathb$ Word.

This Is A Great Sentence With A $\mathc$ Word.

This Is A Great Sentence With A $\mathd$ Word.

This Is A Great Sentence With A $\mathe$ Word.

This Is A Great Sentence With A $\mathf$ Word. I guess this is the right size, too.

{\large This Is A Great Sentence With A $\mathf$ Word. Doesn't grow.}

This Is A Great Sentence With A $\mathg$ Word.

This Is A Great Sentence With A $\mathh$ Word.
\end{document}

Somehow I think, that the first variant is to small. So I tried to enlarge it (in the correct way).

---

My result so far is that I found two solutions, but they do not grow with the rest of the text.

Open questions:

1. Is the second solution "more correct" than the first? Equal? First is better?
2. How to let both fonts grow simultaneously
3. The second argument of fontsize has no effect. (I guess this is may only be in my example) What is the "default" value? / Which value should I use (even if it doesn't matter)

---

Comment: \itshape is only used, because qzcisn't available in upshape

Answer 1

Font sizes are not standardised in the relevant sense. pt in this context is not the standard pt TeX gives you if you ask it to skip a pt to the right or draw a rule so many pts thick or whatever.

When thinking about font sizes, the size of a pt depends on the font. Hence, 12pt is a font-relative size. \normalsize is 12pt for every font in your example, but 12pt is not the same.

To see this, try

\documentclass[border=0pt,multi,tikz]{standalone}
% \usepackage{lmodern}% 3mm x 3mm
% \usepackage{venturis}% 2mm x 2mm
\usepackage[scale=1]{tgchorus}% 2mm x 2mm
\begin{document}
\begin{tikzpicture}[inner sep=0pt]
  \node [draw] {X};
\end{tikzpicture}
\end{document}

Uncommenting the different packages results in a PDF of different sizes. Some are 2mm high; some 3mm.

This is why fonts which are not originally designed to work together typically require scaling in order to create a good result. Some fonts, including Chorus are installed with scaling in mind. In these cases, it is easy to scale the font to match other fonts in the document.

I guess that you want something like this:

{\tiny This Is A Great Sentence With A $\spezial$ Word.\par}

{\scriptsize This Is A Great Sentence With A $\spezial$ Word. I guess this is the right size.\par}

{\footnotesize This Is A Great Sentence With A $\spezial$ Word.\par}

{\small This Is A Great Sentence With A $\spezial$ Word.\par}

{\normalsize This Is A Great Sentence With A $\spezial$ Word.\par}

{\large This Is A Great Sentence With A $\spezial$ Word.\par}

{\Large This Is A Great Sentence With A $\spezial$ Word.\par}

{\LARGE This Is A Great Sentence With A $\spezial$ Word. I guess this is the right size, too.\par}

{\Huge This Is A Great Sentence With A $\spezial$ Word. Doesn't grow.\par}

This Is A Great Sentence With A $\spezial$ Word.

to produce this:

or this:

{\tiny This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\scriptsize This Is A \qzctext{Great} Sentence With A $\spezial$ Word. I guess this is the right size.\par}

{\footnotesize This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\small This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\normalsize This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\large This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\Large This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\LARGE This Is A \qzctext{Great} Sentence With A $\spezial$ Word. I guess this is the right size, too.\par}

{\Huge This Is A \qzctext{Great} Sentence With A $\spezial$ Word. Doesn't grow.\par}

This Is A \qzctext{Great} Sentence With A $\spezial$ Word.

to produce this:

I did this by scaling Chorus using

\newcommand*\qzc@scale{1.2}

My font configuration for Chorus looks like this

\DeclareRobustCommand\qzcstyle{%
  \fontencoding{T1}%
  \fontseries{m}%
  \fontshape{it}%
  \fontfamily{qzc}%
  \selectfont
}

for the basic command and

\DeclareTextFontCommand\qzctext{%
  \qzcstyle
}

for the text command.

For convenience, I defined

\newcommand*\textqzc[1]{\text{\qzctext{#1}}}

for use in maths mode and

\newcommand*\spezial{\textqzc{SPEZIAL}}

for testing.

Note that \text{} is doing important work in maths mode because it invokes \mathchoice to control the size and spacing of the mathematical atom in relation to other atoms.

Compare the two versions. The first is typeset with \textqzc, which uses \text{\qzctext{}}:

\[
  \sum_{\textqzc{i}=1}^n \frac{\textqzc{a}^2 + 3^{\textqzc{b}}}{\textqzc{ab}^2 + n^{\textqzc{a}}}
\]

and second simply uses \qzctext{} directly:

\[
  \sum_{\qzctext{i}=1}^n \frac{\qzctext{a}^2 + 3^{\qzctext{b}}}{\qzctext{ab}^2 + n^{\qzctext{a}}}
\]

Here's the result:

As can be seen, the spacing in the second version is incorrect because \qzctext{} is a text font command and does not make appropriate allowances for spacing in maths mode. The first version, using \text{} invokes \mathchoice to make the required adjustments and the spacing is correct.

Complete code:

\documentclass[a4paper, 12pt]{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{amsmath}
\makeatletter
\newcommand*\qzc@scale{1.2}
\DeclareRobustCommand\qzcstyle{%
  \fontencoding{T1}%
  \fontseries{m}%
  \fontshape{it}%
  \fontfamily{qzc}%
  \selectfont
}
\makeatother
\DeclareTextFontCommand\qzctext{%
  \qzcstyle
}
\newcommand*\textqzc[1]{\text{\qzctext{#1}}}
\newcommand*\spezial{\textqzc{SPEZIAL}}

\begin{document}

% scaled Chorus in maths mode using \text{}

{\tiny This Is A Great Sentence With A $\spezial$ Word.\par}

{\scriptsize This Is A Great Sentence With A $\spezial$ Word. I guess this is the right size.\par}

{\footnotesize This Is A Great Sentence With A $\spezial$ Word.\par}

{\small This Is A Great Sentence With A $\spezial$ Word.\par}

{\normalsize This Is A Great Sentence With A $\spezial$ Word.\par}

{\large This Is A Great Sentence With A $\spezial$ Word.\par}

{\Large This Is A Great Sentence With A $\spezial$ Word.\par}

{\LARGE This Is A Great Sentence With A $\spezial$ Word. I guess this is the right size, too.\par}

{\Huge This Is A Great Sentence With A $\spezial$ Word. Doesn't grow.\par}

This Is A Great Sentence With A $\spezial$ Word.

% scaled Chorus in text and maths modes

{\tiny This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\scriptsize This Is A \qzctext{Great} Sentence With A $\spezial$ Word. I guess this is the right size.\par}

{\footnotesize This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\small This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\normalsize This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\large This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\Large This Is A \qzctext{Great} Sentence With A $\spezial$ Word.\par}

{\LARGE This Is A \qzctext{Great} Sentence With A $\spezial$ Word. I guess this is the right size, too.\par}

{\Huge This Is A \qzctext{Great} Sentence With A $\spezial$ Word. Doesn't grow.\par}

This Is A \qzctext{Great} Sentence With A $\spezial$ Word.
\end{document}