diff --git a/elemcvt.sh b/elemcvt.sh
new file mode 100755
index 0000000..98e8d7f
--- /dev/null
+++ b/elemcvt.sh
@@ -0,0 +1,504 @@
+#! /bin/sh
+# ******************************************************************************
+#  elemcvt: convert NIST "Linear ASCII" table of elements to units(1) format
+#  Usage: elemcvt [options] [<file>]
+#  Author: Jeff Conrad
+#  Date:  2024-01-06
+# ******************************************************************************
+
+# Adjust PATH to suit.
+# For Windows w/MKS Toolkit, this assumes /bin is a symbolic link to
+# $ROOTDIR/mksnt.
+
+PATH=/bin
+
+progname=${0##*[/\\]}
+progname=${progname%.sh}
+export TITLEBAR=$progname
+
+umsg="Usage: $progname [options] [file]
+Options:
+  -d  Show elements for which no standard atomic mass is given and exit
+  -v  Verbose"
+
+show_no_std_atomic_mass=	# show elements for which no std atomic mass is given
+verbose=
+errors=
+DUALCASE=1	# used in MKS Toolkit to make options case sensitive
+
+while getopts :dv arg
+do
+    case $arg in
+    d)
+	show_no_std_atomic_mass=YES ;;
+    v)
+	verbose=YES ;;
+    :)
+	# OPTARG contains the option missing the argument
+	print -ru2 -- "$progname: option $OPTARG requires an argument"
+	errors=YES
+	;;
+    [?])
+	# OPTARG contains the invalid option
+	print -ru2 -- "$progname: unknown option $OPTARG"
+	errors=YES
+	;;
+    esac
+done
+shift $((OPTIND - 1))
+unset DUALCASE
+
+if [ -n "$errors" ]
+then
+    print -ru2 -- "$umsg"
+    exit 1
+fi
+
+awk '
+
+function show_element_info(atomic_number, atomic_symbol, std_atomic_mass_str)
+{
+    printf("# %s: %s (%d)", names[atomic_number], atomic_symbol, atomic_number)
+    if (std_atomic_mass_str)
+	printf("  std atomic weight: %s", std_atomic_mass_str)
+    print ""
+}
+
+# <name>_<atomic num>  <mass> # <mole fraction>
+function show_isotope(name, num)
+{
+    printf("%-*s%*s%*.*f", max_isotope_len, sprintf("%s_%d", name, num),
+	    sepwid, " ", isoprecis + 4, isoprecis, mass[num])
+    if (composition[num])
+	printf("   # %.*f", compprecis, composition[num])
+    print ""
+}
+
+function show_element_name(name)
+{
+    printf("%-*s%*s", max_name_len, name, sepwid, " ")
+}
+
+# <mole fraction> <name>_<mass num>
+function mole_fraction(atomic_number, names, mass_num,  mass_wid)
+{
+    if (composition[mass_num] == 1) {
+	mass_wid = length(int(mass_number[n_isotopes]))
+	# align with 1st digit of atomic mass
+	printf("%*s%s_%d", sepwid + 2 - mass_wid, " ", names[atomic_number], mass_num)
+    }
+    else
+	printf("%.*f %s_%d", compprecis, composition[mass_num],
+		names[atomic_number], mass_num)
+}
+
+# add line continuation and '+' sign
+function add_continuation()
+{
+    printf(" \\\n")
+    printf("%-*s+ ", max_name_len + sepwid - 2, " ")
+}
+
+# <name>_<mass num> # most stable
+function use_most_stable(atomic_number, mass,  mass_wid)
+{
+    mass_wid = length(int(mass_number[n_isotopes]))
+    printf("%*s%-*s   # most stable", sepwid + 2 - mass_wid, " ",
+	    isoprecis + 1 + mass_wid, sprintf("%s_%d", names[atomic_number], mass))
+}
+
+# <name>_<mass num> # standard atomic mass
+function use_std_mass(atomic_number, mass,  mass_wid)
+{
+    mass_wid = length(int(mass_number[n_isotopes]))
+    printf("%*s%-*s   # standard atomic mass", sepwid + 2 - mass_wid, " ",
+	    isoprecis + 1 + mass_wid, sprintf("%s_%d", names[atomic_number], mass))
+}
+
+# show isotopes and the sum of mole fraction-mass products
+function show_element_data(atomic_number, names)
+{
+    # isotopes and relative abundances
+    for (ndx = 1; ndx <= n_isotopes; ndx++) {
+	mass_num = mass_number[ndx]
+	show_isotope(names[atomic_number], mass_num)
+    }
+
+    # show a value for atomic mass if one of these is available;
+    # otherwise, show only isotope masses.
+    if (total_composition > 0 || most_stable_mass || std_atomic_mass)
+	show_element = 1
+    else
+	show_element = 0
+
+    # atomic mass: sum of mole fraction-mass products
+    # element name
+    if (show_element)
+	show_element_name(names[atomic_number])
+
+    mass_num = mass_number[1]
+    firstval = 0
+
+    # first isotope
+    if (composition[mass_num] > 0) {
+	mole_fraction(atomic_number, names, mass_num)
+	firstval = 1
+    }
+    if (n_isotopes > 1) {
+	for (ndx = 2; ndx < n_isotopes; ndx++) {
+	    mass_num = mass_number[ndx]
+	    if (composition[mass_num] > 0) {
+		if (firstval == 1)
+		    add_continuation()
+		mole_fraction(atomic_number, names, mass_num)
+		firstval = 1
+	    }
+	}
+	# last isotope
+	mass_num = mass_number[n_isotopes]
+	if (composition[mass_num] > 0) {
+	    if (firstval == 1)
+		add_continuation()
+	    mole_fraction(atomic_number, names, mass_num)
+	    print ""
+	}
+    }
+    else
+	print ""
+
+    # options if mole fraction is not given for any isotope
+    if (total_composition == 0) {
+	if (most_stable_mass)
+	    use_most_stable(atomic_number, most_stable_mass)
+	else if (std_atomic_mass)
+	    use_std_mass(atomic_number, std_atomic_mass)
+    }
+
+    if (! composition[mass_number[n_isotopes]])
+	print ""
+}
+
+function output(atomic_number)
+{
+    sepwid = 5		# width of column separation
+    compprecis = 8	# for mole fraction
+    isoprecis = 10	# for isotope mass
+
+    # NIST show H, D, and T
+    if (atomic_number == 1)
+	atomic_symbol = "H"
+
+    show_element_info(atomic_number, atomic_symbol, std_atomic_mass_str)
+
+    if (am_names[atomic_number])
+	print "# IUPAC spelling"
+
+    show_element_data(atomic_number, names)
+
+    # show American spelling if different from IUPAC
+    if (am_names[atomic_number]) {
+	print "# American spelling"
+	show_element_data(atomic_number, am_names)
+    }
+    if (show_element)
+	print ""	# blank line between elements
+
+    most_stable_mass = 0
+    total_composition = 0
+}
+
+function gnu_notes()
+{
+    print "\
+# This file is the elements database for use with GNU units, a units\n\
+# conversion program by Adrian Mariano adrianm@gnu.org\n\
+#\n\
+# January 2024 Version 1.0\n\
+#\n\
+# Copyright (C) 2024\n\
+# Free Software Foundation, Inc\n\
+#\n\
+# This program is free software; you can redistribute it and/or modify\n\
+# it under the terms of the GNU General Public License as published by\n\
+# the Free Software Foundation; either version 3 of the License, or\n\
+# (at your option) any later version.\n\
+#\n\
+# This data is distributed in the hope that it will be useful,\n\
+# but WITHOUT ANY WARRANTY; without even the implied warranty of\n\
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the\n\
+# GNU General Public License for more details.\n\
+#\n\
+# You should have received a copy of the GNU General Public License\n\
+# along with this program; if not, write to the Free Software\n\
+# Foundation, Inc., 51 Franklin Street, Fifth Floor,\n\
+# Boston, MA  02110-1301  USA\n"
+}
+
+function nist_notes()
+{
+    print "# From https://www.nist.gov/pml/atomic-weights-and-isotopic-compositions-relative-atomic-masses\n"
+
+    # notes from https://www.nist.gov/pml/atomic-weights-and-isotopic-compositions-column-descriptions
+    print "\
+#   For several elements, the standard atomic weight A_r is given as an\n\
+#   atomic-weight interval with the symbol [a,b] to denote the set of\n\
+#   atomic-weight values in normal materials; thus, [a <= A_r(E) <= b].\n\
+#   The symbols a and b denote the lower and upper bounds of the\n\
+#   interval [a,b], respectively.  The values in parentheses, following\n\
+#   the last significant digit to which they are attributed, are\n\
+#   uncertainties.\n\
+#\n\
+#   Brackets [ ] enclosing a single value indicate the mass number of\n\
+#   the most stable isotope.  For radioactive elements with atomic\n\
+#   numbers 95 or greater, the mass number of the most stable isotope is\n\
+#   not specified, as the list of studied isotopes is still\n\
+#   incomplete.\n"
+}
+
+function units_notes()
+{
+    print "\
+# When composition mole fractions of isotopes are given, the atomic mass\n\
+# of an element is given as the sum of the product(s) of mole\n\
+# fraction(s) and the atomic masses of the relevant isotopes.  When composition\n\
+# mole fractions are not given, the atomic mass is given as\n\
+#\n\
+#   * the mass of the most stable isotope, if available, or\n\
+#   * the standard atomic mass of the element, if available.\n\
+#\n\
+# If neither the most stable isotope nore a standard atomic mass is\n\
+# available, no atomic mass for the element is given; the user must\n\
+# select the isotope most suitable for their purposes.\n\
+#\n\
+# If the standard atomic mass is a range, the value given is the\n\
+# midpoint of that range, which may differ from the value determined\n\
+# from the sum of the products of composition mole fraction and isotope\n\
+# atomic mass.\n"
+}
+
+BEGIN {
+    FS = " *= *"
+    show_no_std_atomic_mass = "'"$show_no_std_atomic_mass"'"
+    verbose = "'"$verbose"'"
+    console = "/dev/console"
+
+    # IUPAC spellings
+    names[1] = "hydrogen"
+    names[2] = "helium"
+    names[3] = "lithium"
+    names[4] = "beryllium"
+    names[5] = "boron"
+    names[6] = "carbon"
+    names[7] = "nitrogen"
+    names[8] = "oxygen"
+    names[9] = "fluorine"
+    names[10] = "neon"
+    names[11] = "sodium"
+    names[12] = "magnesium"
+    names[13] = "aluminium"
+    names[14] = "silicon"
+    names[15] = "phosphorus"
+    names[16] = "sulfur"
+    names[17] = "chlorine"
+    names[18] = "argon"
+    names[19] = "potassium"
+    names[20] = "calcium"
+    names[21] = "scandium"
+    names[22] = "titanium"
+    names[23] = "vanadium"
+    names[24] = "chromium"
+    names[25] = "manganese"
+    names[26] = "iron"
+    names[27] = "cobalt"
+    names[28] = "nickel"
+    names[29] = "copper"
+    names[30] = "zinc"
+    names[31] = "gallium"
+    names[32] = "germanium"
+    names[33] = "arsenic"
+    names[34] = "selenium"
+    names[35] = "bromine"
+    names[36] = "krypton"
+    names[37] = "rubidium"
+    names[38] = "strontium"
+    names[39] = "yttrium"
+    names[40] = "zirconium"
+    names[41] = "niobium"
+    names[42] = "molybdenum"
+    names[43] = "technetium"
+    names[44] = "ruthenium"
+    names[45] = "rhodium"
+    names[46] = "palladium"
+    names[47] = "silver"
+    names[48] = "cadmium"
+    names[49] = "indium"
+    names[50] = "tin"
+    names[51] = "antimony"
+    names[52] = "tellurium"
+    names[53] = "iodine"
+    names[54] = "xenon"
+    names[55] = "caesium"
+    names[56] = "barium"
+    names[57] = "lanthanum"
+    names[58] = "cerium"
+    names[59] = "praseodymium"
+    names[60] = "neodymium"
+    names[61] = "promethium"
+    names[62] = "samarium"
+    names[63] = "europium"
+    names[64] = "gadolinium"
+    names[65] = "terbium"
+    names[66] = "dysprosium"
+    names[67] = "holmium"
+    names[68] = "erbium"
+    names[69] = "thulium"
+    names[70] = "ytterbium"
+    names[71] = "lutetium"
+    names[72] = "hafnium"
+    names[73] = "tantalum"
+    names[74] = "tungsten"
+    names[75] = "rhenium"
+    names[76] = "osmium"
+    names[77] = "iridium"
+    names[78] = "platinum"
+    names[79] = "gold"
+    names[80] = "mercury"
+    names[81] = "thallium"
+    names[82] = "lead"
+    names[83] = "bismuth"
+    names[84] = "polonium"
+    names[85] = "astatine"
+    names[86] = "radon"
+    names[87] = "francium"
+    names[88] = "radium"
+    names[89] = "actinium"
+    names[90] = "thorium"
+    names[91] = "protactinium"
+    names[92] = "uranium"
+    names[93] = "neptunium"
+    names[94] = "plutonium"
+    names[95] = "americium"
+    names[96] = "curium"
+    names[97] = "berkelium"
+    names[98] = "californium"
+    names[99] = "einsteinium"
+    names[100] = "fermium"
+    names[101] = "mendelevium"
+    names[102] = "nobelium"
+    names[103] = "lawrencium"
+    names[104] = "rutherfordium"
+    names[105] = "dubnium"
+    names[106] = "seaborgium"
+    names[107] = "bohrium"
+    names[108] = "hassium"
+    names[109] = "meitnerium"
+    names[110] = "darmstadtium"
+    names[111] = "roentgenium"
+    names[112] = "copernicium"
+    names[113] = "nihonium"
+    names[114] = "flerovium"
+    names[115] = "moscovium"
+    names[116] = "livermorium"
+    names[117] = "tennessine"
+    names[118] = "oganesson"
+
+    # American spellings
+    am_names[13] = "aluminum"
+    am_names[55] = "cesium"
+
+    max_name_len = 0		# length of longest element name
+    for (i = 1; i <= 118; i++) {
+	len = length(names[i])
+	if (len > max_name_len) {
+	    max_name_len = len;
+	    longestname = names[i]
+	}
+    }
+    max_isotope_len = max_name_len + 4	# allow for "_xxx" suffix
+
+    if (! show_no_std_atomic_mass) {
+	gnu_notes()
+	nist_notes()
+	units_notes()
+    }
+
+    if (verbose)
+	printf("Longest element name: %s (%d)\n\n", longestname, max_name_len)
+
+    n_isotopes = 0
+    mass_number[1] = 0
+}
+
+# begin file processing
+
+# skip JavaScript and HTML before data
+NR == 1, $0 ~ /<pre/ { next }
+# skip HTML after data
+$0 ~ /<\/pre>/ { exit }
+
+# remove trailing space and unpaddable spaces
+{ 
+  gsub(/&nbsp;/, "")
+  gsub(/ +$/, "")
+}
+
+$1 ~ /Atomic Number/ {
+    last_atomic_number = atomic_number
+    atomic_number = $2 + 0
+    if (atomic_number != last_atomic_number && atomic_number > 1) {
+	if (show_no_std_atomic_mass) {
+	    if (! std_atomic_mass_str)
+		print names[last_atomic_number]
+	}
+	else
+	    output(last_atomic_number)
+    }
+}
+
+$1 ~ /Atomic Symbol/ {
+    atomic_symbol = $2
+}
+
+$1 ~ /Mass Number/ {
+    if (atomic_number != last_atomic_number) {
+	for (i = 1; i <= n_isotopes; i++)
+	    delete mass_number[i]
+	n_isotopes = 0
+    }
+    mass_number[++n_isotopes] = $2
+}
+
+$1 ~ /Relative Atomic Mass/ {
+    atomic_mass = $2
+    sub(/\([[:digit:]#]+\)/, "", atomic_mass)
+    mass[mass_number[n_isotopes]] = atomic_mass
+}
+
+$1 ~ /Isotopic Composition/ {
+    isotopic_composition = $2
+    sub(/\([[:digit:]#]+\)/, "", isotopic_composition)
+    composition[mass_number[n_isotopes]] = isotopic_composition
+    total_composition += isotopic_composition
+}
+
+$1 ~ /Standard Atomic Weight/ {
+    std_atomic_mass = std_atomic_mass_str = $2
+    gsub(/\([^)]+\)/, "", std_atomic_mass)
+    gsub(/[][]/, "", std_atomic_mass)
+    if (std_atomic_mass ~ /,/) {
+	split(std_atomic_mass, range, /,/)
+	std_atomic_mass = (range[1] + range[2]) / 2
+    }
+    if (std_atomic_mass_str ~ /\[[[:digit:].]+\]/)
+	most_stable_mass = std_atomic_mass
+    last_atomic_number = atomic_number
+}
+
+END {
+    if (show_no_std_atomic_mass) {
+	if (! std_atomic_mass_str)
+	    print names[last_atomic_number]
+    }
+    else
+	output(last_atomic_number)
+} ' $*