diff --git a/davtelepot/messages.py b/davtelepot/messages.py
index 717fc5c..b7b16cf 100644
--- a/davtelepot/messages.py
+++ b/davtelepot/messages.py
@@ -1015,14 +1015,16 @@ default_useful_tools_messages = {
         },
         'help_section': None,
         'instructions': {
-            'en': "🔢 Calculator 🧮\n\n"
+            'en': "🔢 <b>Calculator</b> 🧮\n\n"
                   "Enter an algebraic expression after /calc to get its "
                   "result, or use the command in reply to a message containing "
-                  "an expression, or use the keyboard below.\n",
-            'it': "🔢 Calcolatrice 🧮\n\n"
+                  "an expression, or use the keyboard below.\n\n"
+                  "- <code>ℹ️</code>: show information about special keys\n",
+            'it': "🔢 <b>Calcolatrice</b> 🧮\n\n"
                   "Inserisci un'espressione algebrica dopo /calcola per "
                   "ottenerne il risultato, oppure usa il comando in risposta, "
-                  "o ancora usa la tastiera qui sotto.\n",
+                  "o ancora usa la tastiera qui sotto.\n\n"
+                  "- <code>ℹ️</code>: mostra informazioni sui tasti speciali\n",
         },
         'invalid_expression': {
             'en': "Invalid expression: {error}",
@@ -1032,6 +1034,32 @@ default_useful_tools_messages = {
             'en': "calculate",
             'it': "calcola",
         },
+        'message_input': {
+            'en': "🔢 <b>Calculator</b> 🧮\n\n"
+                  "<i>Enter an expression</i>",
+            'it': "🔢 <b>Calcolatrice</b> 🧮\n\n"
+                  "<i>Mandami l'espressione</i>",
+        },
+        'special_keys': {
+            'en': "<b>Special keys</b>\n"
+                  "- <code>**</code>: exponentiation\n"
+                  "- <code>//</code>: floor division\n"
+                  "- <code>mod</code>: modulus (remainder of division)\n"
+                  "- <code>MR</code>: result of last expression\n"
+                  "- <code>ℹ️</code>: show this help message\n"
+                  "- <code>💬</code>: write your expression in a message\n"
+                  "- <code>⬅️</code>: delete last character\n"
+                  "- <code>✅</code>: start a new line (and a new expression)\n",
+            'it': "<b>Tasti speciali</b>\n"
+                  "- <code>**</code>: elevamento a potenza\n"
+                  "- <code>//</code>: quoziente della divisione\n"
+                  "- <code>mod</code>: resto della divisione\n"
+                  "- <code>MR</code>: risultato dell'espressione precedente\n"
+                  "- <code>ℹ️</code>: mostra questo messaggio\n"
+                  "- <code>💬</code>: invia un messaggio con l'espressione\n"
+                  "- <code>⬅️</code>: cancella ultimo carattere\n"
+                  "- <code>✅</code>: vai a capo (inizia una nuova espressione)\n",
+        },
         'use_buttons': {
             'en': "Use buttons to enter an algebraic expression.\n\n"
                   "<i>The input will be displayed after you stop typing for a "
diff --git a/davtelepot/useful_tools.py b/davtelepot/useful_tools.py
index 2cb4438..29fdc79 100644
--- a/davtelepot/useful_tools.py
+++ b/davtelepot/useful_tools.py
@@ -38,8 +38,8 @@ def get_calc_buttons() -> OrderedDict:
     )
     buttons['_'] = dict(
         value='_',
-        symbol='_️',
-        order='A4',
+        symbol='MR',
+        order='B5',
     )
     buttons[0] = dict(
         value='0',
@@ -129,35 +129,30 @@ def get_calc_buttons() -> OrderedDict:
     buttons['del'] = dict(
         value='del',
         symbol='⬅️',
-        order='F2',
+        order='E5',
     )
     buttons['('] = dict(
         value='(',
         symbol='(️',
-        order='A5',
+        order='A4',
     )
     buttons[')'] = dict(
         value=')',
         symbol=')️',
-        order='B5',
+        order='A5',
     )
-    buttons['m'] = dict(
-        value=')',
-        symbol=')️',
+    buttons['info'] = dict(
+        value='info',
+        symbol='ℹ️️',
         order='C5',
     )
 
-    buttons['u'] = dict(
-        value=')',
-        symbol=')️',
+    buttons['parser'] = dict(
+        value='parser',
+        symbol='💬️',
         order='D5',
     )
 
-    buttons['d'] = dict(
-        value=')',
-        symbol=')️',
-        order='E5',
-    )
     return buttons
 
 
@@ -225,9 +220,11 @@ async def _calculate_button(bot: Bot,
             'useful_tools', 'calculate_command', 'use_buttons',
             language=language
         )
-        reply_markup = get_calculator_keyboard(additional_data=[record_id])
     else:
         record_id = data[0]
+    reply_markup = get_calculator_keyboard(
+        additional_data=([record_id] if record_id else None)
+    )
     if record_id not in bot.shared_data['calc']:
         bot.shared_data['calc'][record_id] = []
         asyncio.ensure_future(
@@ -236,7 +233,35 @@ async def _calculate_button(bot: Bot,
                               language=language)
         )
     update['data'] = data
-    bot.shared_data['calc'][record_id].append(update)
+    if len(data) and data[-1] in ('info', 'parser'):
+        command = data[-1]
+        if command == 'parser':
+            reply_markup = None
+            bot.set_individual_text_message_handler(
+                handler=_calculate_command,
+                user_id=user_record['telegram_id']
+            )
+        elif command == 'info':
+            reply_markup = make_inline_keyboard(
+                [
+                    make_button(
+                        text='Ok',
+                        prefix='calc:///',
+                        delimiter='|',
+                        data=[record_id, 'back']
+                    )
+                ]
+            )
+        text = bot.get_message(
+            'useful_tools', 'calculate_command', (
+                'special_keys' if command == 'info'
+                else 'message_input' if command == 'parser'
+                else ''
+            ),
+            language=language
+        )
+    else:
+        bot.shared_data['calc'][record_id].append(update)
     # Edit the update with the button if a new text is specified
     if not text:
         return
@@ -309,7 +334,7 @@ async def calculate_session(bot: Bot,
     while queue_len != len(queue):
         queue_len = len(queue)
         await asyncio.sleep(buffer_seconds)
-    last_entry = max(queue, key=lambda u: u['id'])
+    last_entry = max(queue, key=lambda u: u['id'], default=None)
     # Delete record-associated queue
     queue = queue.copy()
     del bot.shared_data['calc'][record_id]
@@ -336,6 +361,8 @@ async def calculate_session(bot: Bot,
         input_value = data[1]
         if input_value == 'del':
             expression = expression[:-1]
+        elif input_value == 'back':
+            pass
         elif input_value in calc_buttons:
             expression += calc_buttons[input_value]['value']
         else:
@@ -362,6 +389,8 @@ async def calculate_session(bot: Bot,
             'useful_tools', 'calculate_command', 'instructions',
             language=language
         )
+    if last_entry is None:
+        return
     await bot.edit_message_text(
         text=text,
         update=last_entry,