rntzgeometry.sty

\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{rntzgeometry}[2018/05/10]

%     b6: 125 x 176mm    4.9 x  6.9in
%     a5: 148 x 210mm    5.8 x  8.3in
%     b5: 176 x 250mm    6.9 x  9.8in
%     a4: 210 x 297mm    8.3 x 11.7in
% letter: 216 x 279mm    8.5 x 11in
\DeclareOption{b6}{\def\rntz@geom{b6paper,margin=25pt}}
\DeclareOption{a5}{\def\rntz@geom{a5paper,text={115mm,175mm}}}
\DeclareOption{b5}{\def\rntz@geom{b5paper,text={136mm,205mm}}}
\DeclareOption{a4}{\def\rntz@geom{a4paper,text={160mm,247mm}}}
\DeclareOption{letter}{\def\rntz@geom{letterpaper,text={175mm,230mm}}}

% Based on a bad experience with an HP OfficeJet 6700 printer, 118mm ≈ 335pt
% seems to be about the widest safe area when printing A5 pages 2-up on an A4
% page. Keeping it at 115mm for safety's sake (and for margin scribbles) seems
% prudent.

% Pass unrecognized options to `geometry'.
\DeclareOption*{\PassOptionsToPackage{\CurrentOption}{geometry}}

\ExecuteOptions{a4}
\ProcessOptions\relax

\RequirePackage[\rntz@geom]{geometry}