diff --git a/.gitignore b/.gitignore
index 68c5392..ed13d1c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 releases
 rpn
+rpn.1
diff --git a/Makefile b/Makefile
index 91375f0..69027a4 100644
--- a/Makefile
+++ b/Makefile
@@ -23,8 +23,27 @@ archs     = darwin freebsd linux windows
 PREFIX    = /usr/local
 UID       = root
 GID       = 0
+HAVE_POD := $(shell pod2text -h 2>/dev/null)
 
-all: buildlocal
+all: $(tool).1 $(tool).go buildlocal
+
+%.1: %.pod
+ifdef HAVE_POD
+	  pod2man -c "User Commands" -r 1 -s 1 $*.pod > $*.1
+endif
+
+%.go: %.pod
+ifdef HAVE_POD
+	  echo "package main" > $*.go
+	  echo >> $*.go
+	  echo "var manpage = \`" >> $*.go
+	  pod2text $*.pod >> $*.go
+	  echo "\`" >> $*.go
+
+	  echo "var usage = \`" >> $*.go
+	  awk '/SYNOPS/{f=1;next} /DESCR/{f=0} f' $*.pod  | sed 's/^    //' >> $*.go
+	  echo "\`" >> $*.go
+endif
 
 buildlocal:
 	CGO_LDFLAGS='-static' go build -tags osusergo,netgo -ldflags "-extldflags=-static" -o $(tool)
diff --git a/README.md b/README.md
index 9d24bc7..d3a2d05 100644
--- a/README.md
+++ b/README.md
@@ -16,6 +16,55 @@ Features:
 - can calculate data in batch mode (also from STDIN)
 - extensible with custom LUA functions
 
+## Working principle
+
+Reverse Polish  Notation (short: RPN)  requires to have a  stack where
+numbers and results are being put.  So, you put numbers onto the stack
+and each math  operation uses these for calculation,  removes them and
+puts the result  back.
+
+To visualize it, let's look at a calculation:
+
+    ((80 + 20) / 2) * 4
+    
+This is how  you enter the formula  int an RPN calculator  and how the
+stack evolves during the operation:
+
+| rpn commands | stack contents | calculation   |
+|--------------|----------------|---------------|
+|           80 |             80 |               |
+|           20 |          80 20 |               |
+|            + |            100 | 80 + 20 = 100 |
+|            2 |          100 2 |               |
+|            / |             50 | 100 / 2 = 50  |
+|            4 |           50 4 |               |
+|            x |            200 | 50 * 4 = 200  |
+
+The last stack element 200 is the calculation result. This is how it looks with debugging enabled in `rpn`:
+
+```
+rpn->debug [0/rev0]» 80 20 + 2 / 4 x
+DEBUG(000):      push to stack: 80.00
+DEBUG(001):      push to stack: 20.00
+DEBUG(002):  remove from stack: 20.00
+DEBUG(003):  remove from stack: 80.00
+DEBUG(calc): evaluating: 80.00 + 20.00
+DEBUG(004):      push to stack: 100.00
+= 100
+DEBUG(005):      push to stack: 2.00
+DEBUG(006):  remove from stack: 2.00
+DEBUG(007):  remove from stack: 100.00
+DEBUG(calc): evaluating: 100.00 / 2.00
+DEBUG(008):      push to stack: 50.00
+= 50
+DEBUG(009):      push to stack: 4.00
+DEBUG(010):  remove from stack: 4.00
+DEBUG(011):  remove from stack: 50.00
+DEBUG(calc): evaluating: 50.00 x 4.00
+DEBUG(012):      push to stack: 200.00
+= 200
+```
+
 ## Usage
 
 Basically   you  enter   numbers  followed   by  an   operator  or   a
diff --git a/calc.go b/calc.go
index 6517d08..6e7a445 100644
--- a/calc.go
+++ b/calc.go
@@ -76,9 +76,9 @@ Math operators:
 // commands, constants and operators,  defined here to feed completion
 // and our mode switch in Eval() dynamically
 const (
-	Commands       string = `dump reverse debug undebug clear batch shift undo help history exit quit`
+	Commands       string = `dump reverse debug undebug clear batch shift undo help history manual exit quit`
 	Operators      string = `+ - * x / ^ % %- %+`
-	MathFunctions  string = `sqrt remainder avg mean min max median`
+	MathFunctions  string = `sqrt remainder`
 	Constants      string = `Pi Phi Sqrt2 SqrtE SqrtPi SqrtPhi Ln2 Log2E Ln10 Log10E`
 	BatchFunctions string = `median avg mean max min`
 )
@@ -255,6 +255,8 @@ func (c *Calc) Eval(line string) {
 				fallthrough
 			case "quit":
 				os.Exit(0)
+			case "manual":
+				man()
 			default:
 				fmt.Println("unknown command or operator!")
 			}
diff --git a/main.go b/main.go
index 144c8df..c4da892 100644
--- a/main.go
+++ b/main.go
@@ -18,8 +18,11 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 package main
 
 import (
+	"bytes"
 	"fmt"
+	"log"
 	"os"
+	"os/exec"
 	"strings"
 
 	"github.com/chzyer/readline"
@@ -36,6 +39,7 @@ Usage: rpn [-bdvh] [<operator>]
 Options:
   -b, --batchmode   enable batch mode
   -d, --debug       enable debug mode
+  -m, --manual      show manual
   -v, --version     show version
   -h, --help        show help
 
@@ -49,6 +53,7 @@ func main() {
 
 	showversion := false
 	showhelp := false
+	showmanual := false
 	enabledebug := false
 	configfile := ""
 
@@ -56,6 +61,7 @@ func main() {
 	flag.BoolVarP(&enabledebug, "debug", "d", false, "debug mode")
 	flag.BoolVarP(&showversion, "version", "v", false, "show version")
 	flag.BoolVarP(&showhelp, "help", "h", false, "show usage")
+	flag.BoolVarP(&showmanual, "manual", "m", false, "show manual")
 	flag.StringVarP(&configfile, "config", "c",
 		os.Getenv("HOME")+"/.rpn.lua", "config file (lua format)")
 
@@ -75,6 +81,11 @@ func main() {
 		calc.ToggleDebug()
 	}
 
+	if showmanual {
+		man()
+		os.Exit(0)
+	}
+
 	// the lua state object is global, instanciate it early
 	L = lua.NewState(lua.Options{SkipOpenLibs: true})
 	defer L.Close()
@@ -141,3 +152,20 @@ func inputIsStdin() bool {
 	stat, _ := os.Stdin.Stat()
 	return (stat.Mode() & os.ModeCharDevice) == 0
 }
+
+func man() {
+	man := exec.Command("less", "-")
+
+	var b bytes.Buffer
+	b.Write([]byte(manpage))
+
+	man.Stdout = os.Stdout
+	man.Stdin = &b
+	man.Stderr = os.Stderr
+
+	err := man.Run()
+
+	if err != nil {
+		log.Fatal(err)
+	}
+}
diff --git a/rpn.go b/rpn.go
new file mode 100644
index 0000000..164db2a
--- /dev/null
+++ b/rpn.go
@@ -0,0 +1,206 @@
+package main
+
+var manpage = `
+NAME
+    rpn - Reverse Polish Notation Calculator for the commandline
+
+SYNOPSIS
+        Usage: rpn [-bdvh] [<operator>]
+    
+        Options:
+          -b, --batchmode   enable batch mode
+          -d, --debug       enable debug mode
+          -v, --version     show version
+          -h, --help        show help
+    
+        When <operator>  is given, batch  mode ist automatically  enabled. Use
+        this only when working with stdin. E.g.: echo "2 3 4 5" | rpn +
+
+DESCRIPTION
+    rpn is a command line calculator using reverse polish notation.
+
+  Working principle
+    Reverse Polish Notation (short: RPN) requires to have a stack where
+    numbers and results are being put. So, you put numbers onto the stack
+    and each math operation uses these for calculation, removes them and
+    puts the result back.
+
+    To visualize it, let's look at a calculation:
+
+        ((80 + 20) / 2) * 4
+
+    This is how you enter the formula int an RPN calculator and how the
+    stack evolves during the operation:
+
+        | rpn commands | stack contents | calculation   |
+        |--------------|----------------|---------------|
+        |           80 |             80 |               |
+        |           20 |          80 20 |               |
+        |            + |            100 | 80 + 20 = 100 |
+        |            2 |          100 2 |               |
+        |            / |             50 | 100 / 2 = 50  |
+        |            4 |           50 4 |               |
+        |            x |            200 | 50 * 4 = 200  |
+
+    The last stack element 200 is the calculation result.
+
+  USAGE
+    The default mode of operation is the interactive mode. You'll get a
+    prompt which shows you the current size of the stack. At the prompt you
+    enter numbers followed by operators or mathematical functions. You can
+    use completion for the functions. You can either enter each number or
+    operator on its own line or separated by whitespace, that doesn't
+    matter. After a calculation the result will be immediately displayed
+    (and added to the stack). You can quit interactive mode using the
+    commands quit or exit or hit one of the "ctrl-d" or "ctrl-c" key
+    combinations.
+
+    If you feed data to standard input (STDIN), rpn just does the
+    calculation denoted in the contet fed in via stdin, prints the result
+    and exits. You can also specify a calculation on the commandline.
+
+    Here are the three variants ($ is the shell prompt):
+
+        $ rpn
+        rpn> 2
+        rpn> 2
+        rpn> +
+        = 4
+    
+        $ rpn
+        rpn> 2 2 +
+        = 4
+    
+        $ echo 2 2 + | rpn
+        4
+    
+        $ rpn 2 2 +
+        4
+
+    The rpn calculator provides a batch mode which you can use to do math
+    operations on many numbers. Batch mode can be enabled using the
+    commandline option "-b" or toggled using the interactive command batch.
+    Not all math operations and functions work in batch mode though.
+
+    Example of batch mode usage:
+
+        $ rpn -b
+        rpn->batch > 2 2 2 2 +
+        = 8
+    
+        $ rpn
+        rpn> batch
+        rpn->batch> 2 2 2 2 +
+        8
+    
+        $ echo 2 2 2 2 + | rpn -b
+        8
+    
+        $ echo 2 2 2 2 | rpn +
+        8
+
+    If the first parameter to rpn is a math operator or function, batch mode
+    is enabled automatically, see last example.
+
+  STACK MANIPULATION
+    There are lots of stack manipulation commands provided. The most
+    important one is undo which goes back to the stack before the last math
+    operation.
+
+    You can use dump to display the stack. If debugging is enabled ("-d"
+    switch or debug toggle command), then the backup stack is also being
+    displayed.
+
+    The stack can be reversed using the reverse command.
+
+    You can use the shift command to remove the last number from the stack.
+
+EXTENDING RPN USING LUA
+    You can use a lua script with lua functions to extend the calculator. By
+    default the tool looks for "~/.rpn.lua". You can also specify a script
+    using the <kbd>-c</kbd> flag.
+
+    Here's an example of such a script:
+
+        function add(a,b)
+          return a + b
+        end
+    
+        function init()
+          register("add", 2, "addition")
+        end
+
+    Here we created a function "add()" which adds two parameters. All
+    parameters are "FLOAT64" numbers. You don't have to worry about stack
+    management, this is taken care of automatically.
+
+    The function "init()" MUST be defined, it will be called on startup. You
+    can do anything you like in there, but you need to call the "register()"
+    function to register your functions to the calculator. This function
+    takes these parameters:
+
+    *   function name
+
+    *   number of arguments expected (1,2 or -1 allowed), -1 means batch
+        mode.
+
+    *   help text
+
+    Please refer to the lua language reference:
+    <https://www.lua.org/manual/5.4/> for more details about LUA.
+
+    Please note, that io, networking and system stuff is not allowed though.
+    So you can't open files, execute other programs or open a connection to
+    the outside!
+
+GETTING HELP
+    In interactive mode you can enter the help command (or ?) to get a short
+    help along with a list of all supported operators and functions.
+
+    To read the manual you can use the manual command in interactive mode.
+    The commandline option "-m" does the same thing.
+
+    If you have installed rpn as a package or using the distributed tarball,
+    there will also be a manual page you can read using "man rpn".
+
+BUGS
+    In order to report a bug, unexpected behavior, feature requests or to
+    submit a patch, please open an issue on github:
+    <https://github.com/TLINDEN/rpnc/issues>.
+
+LICENSE
+    This software is licensed under the GNU GENERAL PUBLIC LICENSE version
+    3.
+
+    Copyright (c) 2023 by Thomas von Dein
+
+    This software uses the following GO modules:
+
+    readline (github.com/chzyer/readline)
+        Released under the MIT License, Copyright (c) 2016-2023 ChenYe
+
+    pflag (https://github.com/spf13/pflag)
+        Released under the BSD 3 license, Copyright 2013-2023 Steve Francia
+
+    gopher-lua (github.com/yuin/gopher-lua)
+        Released under the MIT License, Copyright (c) 2015-2023 Yusuke
+        Inuzuka
+
+AUTHORS
+    Thomas von Dein tom AT vondein DOT org
+
+`
+var usage = `
+
+Usage: rpn [-bdvh] [<operator>]
+
+Options:
+  -b, --batchmode   enable batch mode
+  -d, --debug       enable debug mode
+  -v, --version     show version
+  -h, --help        show help
+
+When <operator>  is given, batch  mode ist automatically  enabled. Use
+this only when working with stdin. E.g.: echo "2 3 4 5" | rpn +
+
+`
diff --git a/rpn.pod b/rpn.pod
new file mode 100644
index 0000000..1dea393
--- /dev/null
+++ b/rpn.pod
@@ -0,0 +1,220 @@
+=head1 NAME 
+
+rpn - Reverse Polish Notation Calculator for the commandline
+
+=head1 SYNOPSIS
+
+    Usage: rpn [-bdvh] [<operator>]
+    
+    Options:
+      -b, --batchmode   enable batch mode
+      -d, --debug       enable debug mode
+      -v, --version     show version
+      -h, --help        show help
+    
+    When <operator>  is given, batch  mode ist automatically  enabled. Use
+    this only when working with stdin. E.g.: echo "2 3 4 5" | rpn +
+
+=head1 DESCRIPTION
+
+rpn is a command line calculator using reverse polish notation.
+
+=head2 Working principle
+
+Reverse Polish  Notation (short: RPN)  requires to have a  stack where
+numbers and results are being put.  So, you put numbers onto the stack
+and each math  operation uses these for calculation,  removes them and
+puts the result  back.
+
+To visualize it, let's look at a calculation:
+
+    ((80 + 20) / 2) * 4
+    
+This is how  you enter the formula  int an RPN calculator  and how the
+stack evolves during the operation:
+
+    | rpn commands | stack contents | calculation   |
+    |--------------|----------------|---------------|
+    |           80 |             80 |               |
+    |           20 |          80 20 |               |
+    |            + |            100 | 80 + 20 = 100 |
+    |            2 |          100 2 |               |
+    |            / |             50 | 100 / 2 = 50  |
+    |            4 |           50 4 |               |
+    |            x |            200 | 50 * 4 = 200  |
+
+The last stack element 200 is the calculation result.
+
+=head2 USAGE
+
+The default  mode of operation is  the interactive mode. You'll  get a
+prompt which shows  you the current size of the  stack.  At the prompt
+you enter numbers followed by operators or mathematical functions. You
+can use completion for the functions. You can either enter each number
+or operator on  its own line or separated by  whitespace, that doesn't
+matter. After a  calculation the result will  be immediately displayed
+(and added  to the stack).   You can  quit interactive mode  using the
+commands B<quit> or  B<exit> or hit one of the  C<ctrl-d> or C<ctrl-c>
+key combinations.
+
+If you feed data to standard input (STDIN), rpn just does the
+calculation denoted in the contet fed in via stdin, prints the result
+and exits. You can also specify a calculation on the commandline.
+
+Here are the three variants ($ is the shell prompt):
+
+    $ rpn
+    rpn> 2
+    rpn> 2
+    rpn> +
+    = 4
+    
+    $ rpn
+    rpn> 2 2 +
+    = 4
+    
+    $ echo 2 2 + | rpn
+    4
+    
+    $ rpn 2 2 +
+    4
+
+The rpn calculator provides a batch mode which you can use to do math
+operations on many numbers. Batch mode can be enabled using the
+commandline option C<-b> or toggled using the interactive command
+B<batch>. Not all math operations and functions work in batch mode
+though.
+
+Example of batch mode usage:
+
+    $ rpn -b
+    rpn->batch > 2 2 2 2 +
+    = 8
+    
+    $ rpn
+    rpn> batch
+    rpn->batch> 2 2 2 2 +
+    8
+    
+    $ echo 2 2 2 2 + | rpn -b
+    8
+    
+    $ echo 2 2 2 2 | rpn +
+    8
+    
+
+If the first parameter to rpn is a math operator or function, batch
+mode is enabled automatically, see last example.
+
+=head2 STACK MANIPULATION
+
+There are lots of stack manipulation commands provided. The most
+important one is B<undo> which goes back to the stack before the last
+math operation.
+
+You can use B<dump> to display the stack. If debugging
+is enabled (C<-d> switch or B<debug> toggle command), then the backup
+stack is also being displayed.
+
+The stack can be reversed using the B<reverse> command.
+
+You can use the B<shift> command to remove the last number from the
+stack.
+
+
+=head1 EXTENDING RPN USING LUA
+
+You can use a lua script with lua functions to extend the
+calculator. By default the tool looks for C<~/.rpn.lua>. You can also
+specify a script using the <kbd>-c</kbd> flag.
+
+Here's an example of such a script:
+
+    function add(a,b)
+      return a + b
+    end
+    
+    function init()
+      register("add", 2, "addition")
+    end
+
+Here  we created  a function  C<add()> which  adds two  parameters. All
+parameters are C<FLOAT64> numbers. You  don't have to worry about stack
+management, this is taken care of automatically.
+
+The function C<init()> B<MUST> be defined, it will be called on
+startup. You can do anything you like in there, but you need to call
+the C<register()> function to register your functions to the
+calculator. This function takes these parameters:
+
+=over
+
+=item *
+
+function name
+
+=item *
+
+number of arguments expected (1,2 or -1 allowed), -1 means batch
+mode.
+
+=item *
+
+help text
+
+=back
+
+Please      refer     to      the     lua      language     reference:
+L<https://www.lua.org/manual/5.4/> for more details about LUA.
+
+B<Please note, that io, networking and system stuff is not allowed
+though. So you can't open files, execute other programs or open a
+connection to the outside!>
+
+=head1 GETTING HELP
+
+In interactive mode you can enter the B<help> command (or B<?>) to get
+a short help along with a list of all supported operators and
+functions.
+
+To read the manual you can use the B<manual> command in interactive
+mode. The commandline option C<-m> does the same thing.
+
+If you have installed rpn as a package or using the distributed
+tarball, there will also be a manual page you can read using C<man rpn>.
+
+=head1 BUGS
+
+In order to report a bug, unexpected behavior, feature requests
+or to submit a patch, please open an issue on github:
+L<https://github.com/TLINDEN/rpnc/issues>.
+
+=head1 LICENSE
+
+This software is licensed under the GNU GENERAL PUBLIC LICENSE version 3.
+
+Copyright (c) 2023 by Thomas von Dein
+
+This software uses the following GO modules:
+
+=over 4
+
+=item readline (github.com/chzyer/readline)
+
+Released under the MIT License, Copyright (c) 2016-2023 ChenYe
+
+=item pflag (https://github.com/spf13/pflag)
+
+Released under the BSD 3 license, Copyright 2013-2023 Steve Francia
+
+=item gopher-lua (github.com/yuin/gopher-lua)
+
+Released under the MIT License, Copyright (c) 2015-2023 Yusuke Inuzuka
+
+=back
+
+=head1 AUTHORS
+
+Thomas von Dein B<tom AT vondein DOT org>
+
+=cut