diff --git a/Changes.md b/Changes.md
index de920ba..2bc2c67 100644
--- a/Changes.md
+++ b/Changes.md
@@ -1,4 +1,4 @@
-# Changes in 2.4.0 (WIP)
+# Changes in 2.4.0
 
 IMPORTANT:
 
@@ -18,6 +18,9 @@ Added:
   as a stand-alone library.
 - `helpers.setcall` for registering functions as widget types.
 - `headergen` script for automatic generation of copyright notices.
+- `templates` for the ease of adding new widget types.
+- `CONTRIBUTING.md` which guide contributors through the steps
+  of filing an issue or submitting a patch.
 
 Fixed:
 
diff --git a/README.md b/README.md
index 320d584..edca0e3 100644
--- a/README.md
+++ b/README.md
@@ -864,6 +864,14 @@ mybattery:buttons(awful.util.table.join(
 * [My first awesome](https://awesomewm.org/doc/api/documentation/07-my-first-awesome.md.html)
 
 
+## Contributing
+
+For details, see CONTRIBUTING.md.  Vicious is licensed under GNU GPLv2+,
+which require all code within the package to be released under
+a compatible license.  All contributors retain their copyright to their code,
+so please make sure you add your name to the header of every file you touch.
+
+
 ## Authors
 
 Wicked was written by:
diff --git a/headergen b/headergen
index 8170cf5..fe3dd51 100755
--- a/headergen
+++ b/headergen
@@ -1,6 +1,6 @@
 #!/usr/bin/env lua
 -- copyright header generator
--- Copyright (C) 2019  Nguyễn Gia Phong
+-- Copyright (C) 2019  Nguyễn Gia Phong <vn.mcsinyx@gmail.com>
 --
 -- This file is part of Vicious.
 --
diff --git a/helpers.lua b/helpers.lua
index 9598a12..bbe6da1 100644
--- a/helpers.lua
+++ b/helpers.lua
@@ -123,9 +123,9 @@ end
 -- }}}
 
 -- {{{ Set widget type's __call metamethod to given worker function
-function helpers.setcall(wtype, worker)
+function helpers.setcall(worker)
     return setmetatable(
-        wtype, { __call = function(_, ...) return worker(...) end })
+        {}, { __call = function(_, ...) return worker(...) end })
 end
 -- }}}
 
@@ -285,5 +285,4 @@ end
 --  }}}
 
 return helpers
-
 -- }}}
diff --git a/init.lua b/init.lua
index 10a5865..e4f7568 100644
--- a/init.lua
+++ b/init.lua
@@ -35,7 +35,7 @@
 local type  = type
 local pairs = pairs
 local tonumber = tonumber
-local timer = (type(timer) == 'table' and timer or require("gears.timer"))
+local timer = type(timer) == "table" and timer or require("gears.timer")
 local os    = { time = os.time }
 local table = {
     insert  = table.insert,
@@ -94,20 +94,22 @@ local function update(widget, reg, disablecache)
         return ret or data
     end
 
+    local function topercent(e) return tonumber(e) and tonumber(e) / 100 end
+
     local function update_value(data)
         local fmtd_data = format_data(data)
         if widget.add_value ~= nil then
             if widget.get_stack ~= nil and widget:get_stack() then
                 for idx, _ in ipairs(widget:get_stack_colors()) do
                     if fmtd_data[idx] then
-                        widget:add_value(tonumber(fmtd_data[idx]) and tonumber(fmtd_data[idx]/100), idx)
+                        widget:add_value(topercent(fmtd_data[idx]), idx)
                     end
                 end
             else
-                widget:add_value(tonumber(fmtd_data) and tonumber(fmtd_data)/100)
+                widget:add_value(topercent(fmtd_data))
             end
         elseif widget.set_value ~= nil then
-            widget:set_value(tonumber(fmtd_data) and tonumber(fmtd_data)/100)
+            widget:set_value(topercent(fmtd_data))
         elseif widget.set_markup ~= nil then
             widget:set_markup(fmtd_data)
         else
diff --git a/templates/async.lua b/templates/async.lua
index ebc2308..d704071 100644
--- a/templates/async.lua
+++ b/templates/async.lua
@@ -1,5 +1,5 @@
 -- template for asynchronous widet types
--- Copyright (C) 2019  Nguyễn Gia Phong
+-- Copyright (C) 2019  Nguyễn Gia Phong <vn.mcsinyx@gmail.com>
 --
 -- This file is part of Vicious.
 --
diff --git a/templates/sync.lua b/templates/sync.lua
index 6b2b15f..4b49059 100644
--- a/templates/sync.lua
+++ b/templates/sync.lua
@@ -1,5 +1,5 @@
 -- template for synchronous widet types
--- Copyright (C) 2019  Nguyễn Gia Phong
+-- Copyright (C) 2019  Nguyễn Gia Phong <vn.mcsinyx@gmail.com>
 --
 -- This file is part of Vicious.
 --
diff --git a/widgets/bat_linux.lua b/widgets/bat_linux.lua
index 39352b4..186c6e8 100644
--- a/widgets/bat_linux.lua
+++ b/widgets/bat_linux.lua
@@ -31,12 +31,8 @@ local math = {
 local helpers = require"vicious.helpers"
 -- }}}
 
--- Bat: provides state, charge, remaining time, and wear for a requested battery
--- vicious.widgets.bat
-local bat_linux = {}
-
 -- {{{ Battery widget type
-local function worker(format, warg)
+return helpers.setcall(function (format, warg)
     if not warg then return end
 
     local battery = helpers.pathtotable("/sys/class/power_supply/"..warg)
@@ -109,7 +105,5 @@ local function worker(format, warg)
     end
 
     return {state, percent, time, wear, curpower}
-end
+end)
 -- }}}
-
-return helpers.setcall(bat_linux, worker)
diff --git a/widgets/cpu_linux.lua b/widgets/cpu_linux.lua
index 3ac8734..c023400 100644
--- a/widgets/cpu_linux.lua
+++ b/widgets/cpu_linux.lua
@@ -32,17 +32,13 @@ local string = {
 local helpers = require"vicious.helpers"
 -- }}}
 
--- Cpu: provides CPU usage for all available CPUs/cores
--- vicious.widgets.cpu
-local cpu_linux = {}
-
 -- Initialize function tables
 local cpu_usage  = {}
 local cpu_total  = {}
 local cpu_active = {}
 
 -- {{{ CPU widget type
-local function worker(format)
+return helpers.setcall(function ()
     local cpu_lines = {}
 
     -- Get CPU stats
@@ -86,7 +82,5 @@ local function worker(format)
     end
 
     return cpu_usage
-end
+end)
 -- }}}
-
-return helpers.setcall(cpu_linux, worker)
diff --git a/widgets/cpufreq_linux.lua b/widgets/cpufreq_linux.lua
index b956bf3..f3877e4 100644
--- a/widgets/cpufreq_linux.lua
+++ b/widgets/cpufreq_linux.lua
@@ -22,10 +22,6 @@ local tonumber = tonumber
 local helpers = require("vicious.helpers")
 -- }}}
 
--- Cpufreq: provides freq, voltage and governor info for a requested CPU
--- vicious.widgets.cpufreq
-local cpufreq_linux = {}
-
 local GOVERNOR_STATE = {
     ["ondemand\n"]     = "↯",
     ["powersave\n"]    = "⌁",
@@ -35,7 +31,7 @@ local GOVERNOR_STATE = {
 }
 
 -- {{{ CPU frequency widget type
-local function worker(format, warg)
+return helpers.setcall(function (format, warg)
     if not warg then return end
 
     local _cpufreq = helpers.pathtotable(
@@ -68,7 +64,5 @@ local function worker(format, warg)
     governor = GOVERNOR_STATE[governor] or governor or "N/A"
 
     return {freqv.mhz, freqv.ghz, freqv.mv, freqv.v, governor}
-end
+end)
 -- }}}
-
-return helpers.setcall(cpufreq_linux, worker)
diff --git a/widgets/cpuinf_linux.lua b/widgets/cpuinf_linux.lua
index afb5ce2..0df845f 100644
--- a/widgets/cpuinf_linux.lua
+++ b/widgets/cpuinf_linux.lua
@@ -24,12 +24,8 @@ local string = { gmatch = string.gmatch }
 local helpers = require"vicious.helpers"
 -- }}}
 
--- Cpuinf: provides speed and cache information for all available CPUs/cores
--- vicious.widgets.cpuinf
-local cpuinf_linux = {}
-
 -- {{{ CPU Information widget type
-local function worker(format)
+return helpers.setcall(function ()
     local id = nil
 
     local cpu_info = {} -- Get CPU info
@@ -50,7 +46,5 @@ local function worker(format)
     end
 
     return cpu_info
-end
+end)
 -- }}}
-
-return helpers.setcall(cpuinf_linux, worker)
diff --git a/widgets/date_all.lua b/widgets/date_all.lua
index 0c29c80..459d505 100644
--- a/widgets/date_all.lua
+++ b/widgets/date_all.lua
@@ -24,6 +24,6 @@ local os = { date = os.date, time = os.time }
 local helpers = require"vicious.helpers"
 -- }}}
 
-return helpers.setcall({}, function (format, warg)
+return helpers.setcall(function (format, warg)
     return os.date(format or nil, warg and os.time()+warg or nil)
 end)
diff --git a/widgets/dio_linux.lua b/widgets/dio_linux.lua
index 25d2578..60c2343 100644
--- a/widgets/dio_linux.lua
+++ b/widgets/dio_linux.lua
@@ -26,10 +26,6 @@ local os = { time = os.time, difftime = os.difftime }
 local helpers = require"vicious.helpers"
 -- }}}
 
--- Disk I/O: provides I/O statistics for requested storage devices
--- vicious.widgets.dio
-local dio_linux = {}
-
 -- Initialize function tables
 local disk_usage = {}
 local disk_stats = {}
@@ -39,7 +35,7 @@ local unit = { ["s"] = 1, ["kb"] = 2, ["mb"] = 2048 }
 local time_unit = { ["ms"] = 1, ["s"] = 1000 }
 
 -- {{{ Disk I/O widget type
-local function worker(format)
+return helpers.setcall(function ()
     local disk_lines = {}
 
     for line in io.lines("/proc/diskstats") do
@@ -79,7 +75,5 @@ local function worker(format)
     disk_stats = disk_lines
 
     return disk_usage
-end
+end)
 -- }}}
-
-return helpers.setcall(dio_linux, worker)
diff --git a/widgets/mbox_all.lua b/widgets/mbox_all.lua
index f5f9a6a..d65fac8 100644
--- a/widgets/mbox_all.lua
+++ b/widgets/mbox_all.lua
@@ -24,14 +24,11 @@ local io = { open = io.open }
 local helpers = require("vicious.helpers")
 -- }}}
 
--- vicious.widgets.mbox
-local mbox_all = {}
-
 -- Initialize variables
 local subject = "N/A"
 
 -- {{{ Mailbox widget type
-local function worker(format, warg)
+return helpers.setcall(function (format, warg)
     if not warg then return end
 
     local f = io.open(type(warg) == "table" and warg[1] or warg)
@@ -54,7 +51,5 @@ local function worker(format, warg)
     end
 
     return { subject }
-end
+end)
 -- }}}
-
-return helpers.setcall(mbox_all, worker)
diff --git a/widgets/mboxc_all.lua b/widgets/mboxc_all.lua
index f9e8b6a..ab33a0d 100644
--- a/widgets/mboxc_all.lua
+++ b/widgets/mboxc_all.lua
@@ -22,11 +22,8 @@ local io = { open = io.open }
 local helpers = require"vicious.helpers"
 -- }}}
 
--- vicious.widgets.mboxc
-local mboxc_all = {}
-
 -- {{{ Mbox count widget type
-local function worker(format, warg)
+return helpers.setcall(function (format, warg)
     if not warg then return end
 
     -- Initialize counters
@@ -62,7 +59,5 @@ local function worker(format, warg)
     count.new = count.total - count.old
 
     return {count.total, count.old, count.new}
-end
+end)
 -- }}}
-
-return helpers.setcall(mboxc_all, worker)
diff --git a/widgets/mem_linux.lua b/widgets/mem_linux.lua
index e49c106..318b51f 100644
--- a/widgets/mem_linux.lua
+++ b/widgets/mem_linux.lua
@@ -26,12 +26,8 @@ local string = { gmatch = string.gmatch }
 local helpers = require"vicious.helpers"
 -- }}}
 
--- Mem: provides RAM and Swap usage statistics
--- vicious.widgets.mem
-local mem_linux = {}
-
 -- {{{ Memory widget type
-local function worker(format)
+return helpers.setcall(function ()
     local _mem = { buf = {}, swp = {} }
 
     -- Get MEM info
@@ -60,7 +56,5 @@ local function worker(format)
     return {_mem.usep,     _mem.inuse,     _mem.total, _mem.free,
             _mem.swp.usep, _mem.swp.inuse, _mem.swp.t, _mem.swp.f,
             _mem.bcuse }
-end
+end)
 -- }}}
-
-return helpers.setcall(mem_linux, worker)
diff --git a/widgets/net_linux.lua b/widgets/net_linux.lua
index 5ee01d8..612da4d 100644
--- a/widgets/net_linux.lua
+++ b/widgets/net_linux.lua
@@ -26,10 +26,6 @@ local string = { match = string.match }
 local helpers = require("vicious.helpers")
 -- }}}
 
--- Net: provides state and usage statistics of all network interfaces
--- vicious.widgets.net
-local net_linux = {}
-
 -- Initialize function tables
 local nets = {}
 -- Variable definitions
@@ -38,7 +34,7 @@ local unit = { ["b"] = 1, ["kb"] = 1024,
 }
 
 -- {{{ Net widget type
-local function worker(format)
+return helpers.setcall(function ()
     local args = {}
 
     -- Get NET stats
@@ -85,7 +81,5 @@ local function worker(format)
     end
 
     return args
-end
+end)
 -- }}}
-
-return helpers.setcall(net_linux, worker)
diff --git a/widgets/org_all.lua b/widgets/org_all.lua
index 44be341..b15fd16 100644
--- a/widgets/org_all.lua
+++ b/widgets/org_all.lua
@@ -24,12 +24,8 @@ local os = { time = os.time, date = os.date }
 local helpers = require"vicious.helpers"
 -- }}}
 
--- Org: provides agenda statistics for Emacs org-mode
--- vicious.widgets.org
-local org_all = {}
-
 -- {{{ OrgMode widget type
-local function worker(format, warg)
+return helpers.setcall(function (format, warg)
     if not warg then return end
 
     -- Compute delays
@@ -65,7 +61,5 @@ local function worker(format, warg)
     end
 
     return { count.past, count.today, count.soon, count.future }
-end
+end)
 -- }}}
-
-return helpers.setcall(org_all, worker)
diff --git a/widgets/os_linux.lua b/widgets/os_linux.lua
index 08bba41..a1528e5 100644
--- a/widgets/os_linux.lua
+++ b/widgets/os_linux.lua
@@ -28,12 +28,8 @@ local string = { gsub = string.gsub }
 local helpers = require"vicious.helpers"
 -- }}}
 
--- OS: provides operating system information
--- vicious.widgets.os
-local os_linux = {}
-
 -- {{{ Operating system widget type
-local function worker(format)
+return helpers.setcall(function ()
     local system = {
         ["ostype"]    = "N/A",
         ["hostname"]  = "N/A",
@@ -66,7 +62,5 @@ local function worker(format)
 
     return {system["ostype"], system["osrelease"], system["username"],
             system["hostname"], system["entropy"], system["entropy_p"]}
-end
+end)
 -- }}}
-
-return helpers.setcall(os_linux, worker)
diff --git a/widgets/raid_linux.lua b/widgets/raid_linux.lua
index f88f29e..7b4d23f 100644
--- a/widgets/raid_linux.lua
+++ b/widgets/raid_linux.lua
@@ -29,15 +29,11 @@ local string = {
 local helpers = require"vicious.helpers"
 -- }}}
 
--- Raid: provides state information for a requested RAID array
--- vicious.widgets.raid
-local raid_linux = {}
-
 -- Initialize function tables
 local mddev = {}
 
 -- {{{ RAID widget type
-local function worker(format, warg)
+return helpers.setcall(function (format, warg)
     if not warg then return end
     mddev[warg] = {
         ["found"]    = false,
@@ -67,7 +63,5 @@ local function worker(format, warg)
     f:close()
 
     return {mddev[warg]["assigned"], mddev[warg]["active"]}
-end
+end)
 -- }}}
-
-return helpers.setcall(raid_linux, worker)
diff --git a/widgets/thermal_linux.lua b/widgets/thermal_linux.lua
index fc8ece9..7ac8e69 100644
--- a/widgets/thermal_linux.lua
+++ b/widgets/thermal_linux.lua
@@ -25,12 +25,8 @@ local math = { floor = math.floor }
 local helpers = require("vicious.helpers")
 -- }}}
 
--- Thermal: provides temperature levels of ACPI and coretemp thermal zones
--- vicious.widgets.thermal
-local thermal_linux = {}
-
 -- {{{ Thermal widget type
-local function worker(format, warg)
+return helpers.setcall(function (format, warg)
     if not warg then return end
 
     local zone = { -- Known temperature data sources
@@ -54,7 +50,5 @@ local function worker(format, warg)
     end
 
     return {0}
-end
+end)
 -- }}}
-
-return helpers.setcall(thermal_linux, worker)
diff --git a/widgets/uptime_linux.lua b/widgets/uptime_linux.lua
index 1c340a6..7ff3580 100644
--- a/widgets/uptime_linux.lua
+++ b/widgets/uptime_linux.lua
@@ -24,12 +24,8 @@ local string = { match = string.match }
 local helpers = require("vicious.helpers")
 -- }}}
 
--- Uptime: provides system uptime and load information
--- vicious.widgets.uptime
-local uptime_linux = {}
-
 -- {{{ Uptime widget type
-local function worker(format)
+return helpers.setcall(function ()
     local proc = helpers.pathtotable("/proc")
 
     -- Get system uptime
@@ -41,7 +37,5 @@ local function worker(format)
     local l1, l5, l15 = -- Get load averages for past 1, 5 and 15 minutes
         string.match(proc.loadavg, "([%d%.]+)[%s]([%d%.]+)[%s]([%d%.]+)")
     return {up_d, up_h, up_m, l1, l5, l15}
-end
+end)
 -- }}}
-
-return helpers.setcall(uptime_linux, worker)