I enclosed the code for two calstable
s, typeset with the help of the package cals.
The first table is typeset with vertical rules. Due to the width of the headers, I reduced margins with the help of geometry.
I have aligned the second row headers at the bottom of the cells, the content of all other cells are centred vertically. Also, the font size used in the header is reduced, making the them less dominant and disturbing.
The second calstable
is typeset without vertical rules. As yo will find, those are unnecessary for the readability.

\documentclass[12pt,oneside,letterpaper]{book}
\usepackage{lmodern, cals}
\usepackage[left=3cm, right=3cm]{geometry}
% Set up the carlstable
\makeatletter
%% All rules of same weight
\def\cals@framers@width{0.4pt} % Outside frame rules, reduce if the rule is too heavy
\def\cals@framecs@width{0.4pt}
\def\cals@bodyrs@width{0.4pt}
\def\cals@AtBeginCell{\vfil} % All cell contents vertically centred
% Shorthands for spanning cells
\let\nc=\nullcell
\let\sc=\spancontent
\def\rb{\ifx\cals@borderR\relax % Right Border (rules) switch (off-on)
\def\cals@borderR{0.0pt}
\else \let\cals@borderR\relax\fi}
\def\lb{\ifx\cals@borderL\relax % Left Border switch (off-on)
\def\cals@borderL{0.0pt}
\else \let\cals@borderL\relax\fi}
\def\bb{\ifx\cals@borderB\relax % Bottom Border switch (off-on)
\def\cals@borderB{0.0pt}
\else \let\cals@borderB\relax\fi}
\def\lp{\ifdim\cals@paddingL=0.0pt\relax % Left padding switch (off-on)
\setlength{\cals@paddingL}{3pt}
\else \setlength{\cals@paddingL}{0pt}\fi}
\def\rp{\ifdim\cals@paddingR=0.0pt\relax % Right padding switch (off-on)
\setlength{\cals@paddingR}{3pt}
\else \setlength{\cals@paddingR}{0.0pt}\fi}
\makeatother
\begin{document}
\begin{calstable}[c]
% Defining 5 columns, 1 are for double vertical rules (col2)
\colwidths{{\dimexpr(\columnwidth/50*7+8pt)}
{\dimexpr(\columnwidth/50*7-5pt)}
{\dimexpr(\columnwidth/50*7-5pt)}
{\dimexpr(\columnwidth/50*9)}
{\dimexpr(\columnwidth/50*10+2pt)}
{\dimexpr(\columnwidth/50*9)}
}
\makeatletter
\setlength{\cals@paddingL}{2pt} % Changes to padding has to go inside the tables preamble
\setlength{\cals@paddingR}{2pt} % Decrease tabcolsep from 4.96pt to 2pt
\setlength{\cals@paddingB}{3pt} % Uncomment if you want less space between cells
%\setlength{\cals@paddingT}{2pt}
% R1H1
\thead{\footnotesize%
\brow
\nc{lrt}
\nc{ltb}
\nc{rtb}\alignC\sc{Magnetic Flux}
\nc{lrt}
\nc{lrt}
\nc{lrt}
\erow
%
%R2H2 % Header
\brow
\nc{lrb}\alignC\sc{Action}
\cell{\vfill Direction\\ (Up/Down)}
\cell{\vfill Increasing/\\ Decreasing}
\nc{lrb}\alignC\sc{\vfill Direction of\\Induced $B$\\\mbox{Field (Expected)}}
\nc{lrb}\alignC\sc{\vfill \mbox{Expected Direction}\\\mbox{of Induced Current}\\(CW/CCW)}
\nc{lrb}\alignC\sc{\vfill\mbox{Actual Direction}\\of Induced\\Current\vphantom{j}} % \vphantom command since Current has no depth
\erow
}
\tfoot{\lastrule\strut}
\small
%R3B1
\brow
\alignL\cell{N pole in}
\cell{}
\cell{}
\cell{}
\cell{}
\cell{}
\erow
%R4B2
\brow
\alignL\cell{N pole out}
\cell{}
\cell{}
\cell{}
\cell{}
\cell{}
\erow
%R5B3
\brow
\alignL\cell{S pole in}
\cell{}
\cell{}
\cell{}
\cell{}
\cell{}
\erow
%R6B4
\brow
\alignL\cell{S pole out}
\cell{}
\cell{}
\cell{}
\cell{}
\cell{}
\erow
\makeatletter
\end{calstable}\par
\vspace{1cm}
\begin{calstable}[c]
% Defining 5 columns, 1 are for double vertical rules (col2)
\colwidths{{\dimexpr(\columnwidth/50*7+8pt)}
{\dimexpr(\columnwidth/50*7-5pt)}
{\dimexpr(\columnwidth/50*7-5pt)}
{\dimexpr(\columnwidth/50*9)}
{\dimexpr(\columnwidth/50*10+2pt)}
{\dimexpr(\columnwidth/50*9)}
}
\makeatletter
%% All rules of same weight
\def\cals@framers@width{0.8pt} % Outside frame rules, reduce if the rule is too heavy
\def\cals@framecs@width{0.0pt}
\def\cals@bodyrs@width{0.6pt}
\def\cals@cs@width{0.0pt} % Inside rules, reduce if the rule is too heavy
\def\cals@rs@width{0.3pt}
\def\cals@AtBeginCell{\vfil} % All cell contents vertically centred
\setlength{\cals@paddingL}{3pt} % Changes to padding has to go inside the tables preamble
\setlength{\cals@paddingR}{3pt} % Decrease tabcolsep from 4.96pt to 2pt
\setlength{\cals@paddingB}{3pt} % Uncomment if you want less space between cells
%\setlength{\cals@paddingT}{2pt}
% R1H1
\thead{\footnotesize%
\brow
\lp\nc{lrt}\lp
\nc{ltb}
\nc{rtb}\alignC\sc{Magnetic Flux}
\nc{lrt}
\nc{lrt}
\rp\nc{lrt}\rp
\erow
%
%R2H2 % Header
\brow
\lp\nc{lrb}\alignC\sc{Action}\lp
\cell{\vfill Direction\\ (Up/Down)}
\cell{\vfill Increasing/\\ Decreasing}
\nc{lrb}\alignC\sc{\vfill Direction of\\Induced $B$\\\mbox{Field (Expected)}}
\nc{lrb}\alignC\sc{\vfill \mbox{Expected Direction}\\\mbox{of Induced Current}\\(CW/CCW)}
\rp\nc{lrb}\alignC\sc{\vfill\mbox{Actual Direction}\\of Induced\\Current\vphantom{j}}\rp % \vphantom command since Current has no depth
\erow
}
\tfoot{\lastrule\strut}
\small
%R3B1
\brow
\lp\bb\alignL\cell{N pole in}\lp
\cell{}
\cell{}
\cell{}
\cell{}
\rp\cell{}\rp
\erow
%R4B2
\brow
\lp\alignL\cell{N pole out}\lp
\cell{}
\cell{}
\cell{}
\cell{}
\rp\cell{}\rp
\erow
%R5B3
\brow
\lp\alignL\cell{S pole in}\lp
\cell{}
\cell{}
\cell{}
\cell{}
\rp\cell{}\bb\rp
\erow
%R6B4
\brow
\lp\alignL\cell{S pole out}\lp
\cell{}
\cell{}
\cell{}
\cell{}
\rp\cell{}\rp
\erow
\makeatletter
\end{calstable}\par
\end{document}
\end{document}