--- a/scripts/control/base/nichols.m
+++ b/scripts/control/base/nichols.m
@@ -20,35 +20,65 @@
 ## @deftypefn {Function File} {[@var{mag}, @var{phase}, @var{w}] =} nichols (@var{sys}, @var{w}, @var{outputs}, @var{inputs})
 ## Produce Nichols plot of a system.
 ##
-## inputs:
-##   sys: system data structure (must be either purely continuous or discrete;
-##       see is_digital)
-##   w: frequency values for evaluation.
-##      if sys is continuous, then nichols evaluates G(jw)
-##      if sys is discrete, then nichols evaluates G(exp(jwT)), where T=sys.tsam
-##         (the system sampling time)
-##      default: the default frequency range is selected as follows: (These
-##        steps are NOT performed if w is specified)
-##          (1) via routine __bodquist__, isolate all poles and zeros away from
-##              w=0 (jw=0 or exp(jwT)=1) and select the frequency
-##             range based on the breakpoint locations of the frequencies.
-##          (2) if sys is discrete time, the frequency range is limited
-##              to jwT in [0,2p*pi]
-##          (3) A "smoothing" routine is used to ensure that the plot phase does
-##              not change excessively from point to point and that singular
-##              points (e.g., crossovers from +/- 180) are accurately shown.
-##   outputs, inputs: the names or indices of the output(s) and input(s) 
-##     to be used in the frequency response; see sysprune.
-## outputs:
-##    mag, phase: the magnitude and phase of the frequency response
-##       G(jw) or G(exp(jwT)) at the selected frequency values.
-##    w: the vector of frequency values used
-## If no output arguments are given, nichols plots the results to the screen.
-## Descriptive labels are automatically placed.  See xlabel, ylable, title,
-## and replot.
+## @strong{Inputs}
+## @table @var
+## @item sys
+## System data structure (must be either purely continuous or discrete; 
+## see @command{is_digital}).
+## @item w
+## Frequency values for evaluation.
+## @itemize
+## @item if sys is continuous, then nichols evaluates @math{G(jw)}.
+## @item if sys is discrete, then nichols evaluates @math{G(exp(jwT))}, 
+## where @var{T}=@var{sys}. @var{tsam} is the system sampling time.
+## @item the default frequency range is selected as follows (These
+##        steps are @strong{not} performed if @var{w} is specified):
+## @enumerate
+## @item via routine @command{__bodquist__}, isolate all poles and zeros away from
+## @var{w}=0 (@math{jw=0} or @math{exp(jwT)=1}) and select the frequency range 
+## based on the breakpoint locations of the frequencies.
+## @item if sys is discrete time, the frequency range is limited to jwT in 
+## @iftex
+## @tex
+## $ [0, 2p\pi] $.
+## @end tex
+## @end iftex
+## @ifinfo
+## [0,2p*pi].
+## @end ifinfo
+## @item A ``smoothing'' routine is used to ensure that the plot phase does
+## not change excessively from point to point and that singular points 
+## (e.g., crossovers from +/- 180) are accurately shown.
+## @end enumerate
+## @end itemize
+## @item outputs
+## @itemx inputs
+## the names or indices of the output(s) and input(s) to be used in the 
+## frequency response; see @command{sysprune}.
+## @end table
+## @strong{Outputs}
+## @table @var
+## @item mag
+## @itemx phase
+## The magnitude and phase of the frequency response @math{G(jw)} or 
+## @math{G(exp(jwT))} at the selected frequency values.
+## @item w
+## The vector of frequency values used.
+## @end table
+## If no output arguments are given, @command{nichols} plots the results to the screen.
+## Descriptive labels are automatically placed. See @command{xlabel}, 
+## @command{ylabel}, @command{title}, and @command{replot}.
 ##
-## Note: if the requested plot is for an MIMO system, mag is set to
-## ||G(jw)|| or ||G(exp(jwT))|| and phase information is not computed.
+## Note: if the requested plot is for an @acronym{MIMO} system, @var{mag} is set to
+## @iftex
+## @tex
+## $ \Vert G(jw) \Vert $ or $ \Vert G( {\rm exp}(jwT) \Vert $
+## @end tex
+## @end iftex
+## @ifinfo
+## ||G(jw)|| or ||G(exp(jwT))||
+## @end ifinfo
+## and phase information is not computed.
 ## @end deftypefn
 
 function [mag, phase, w] = nichols (sys, w, outputs, inputs)