Hardware conttrol panels historically have used several types of meters. Tcl/Tk widgets have already been written for what I would call 'angular meters'. That is a meter whose needle shows the value of the data it is monitoring through it's angle. A more common meter in the control panels where I work is a 'vertical' meter. Think of this as a vertical rectangle with a tick mark scalen and a needle that shows the value of the data it is monitoring by its height in the rectangle.
Here's a snit::widget that is my first cut at implementing a 'vertical' meter (still a few edge issues with tick marks):
#
# This software is Copyright by the Board of Trustees of Michigan
# State University (c) Copyright 2005.
#
# You may use this software under the terms of the GNU public license
# (GPL). The terms of this license are described at:
#
# http://www.gnu.org/licenses/gpl.txt
#
# Author:
# Ron Fox
# NSCL
# Michigan State University
# East Lansing, MI 48824-1321
#
# Implements a 'meter' megawidget. A meter is a
# box with a needle that goes up and down between
# two possible limits.
#
# This is drawn in a canvas as follows:
# +-------+
# | |
# | <----|
# | ...
# +-------+
#
#
# OPTIONS:
# -from - Value represented by the lower limit of the meter. (dynamic)
# -to - Value represented by the upper limit of the meter. (dynamic)
# -height - Height of the meter. (static)
# -width - Width of the meter. (static)
# -variable - Variable the meter will track. (dynamic)
# -majorticks - Interval between major (labelled) ticks. (dynamic)
# -minorticks - Number of minor ticks drawn between major ticks. (dynamic)
#
# Methods:
# set value - Set the meter to a specific value (if -variable is defined it is modified).
# get - Returns the current value of the meter.
package provide meter 1.0
package require Tk
package require snit
namespace eval controlwidget {
namespace export meter
}