diff --git a/examples/custom_m_codes.py b/examples/custom_m_codes.py
index 8a78f20..af43ac9 100755
--- a/examples/custom_m_codes.py
+++ b/examples/custom_m_codes.py
@@ -12,6 +12,25 @@
 from dsf.commands.code import CodeType
 from dsf.object_model import MessageType
 
+# needed to resolve meta variables
+from dsf.connections import CommandConnection
+from dsf.commands.generic import evaluate_expression
+
+
+# function to ask RRF to resolve a meta variable
+def eval_expr( meta_var, channel):
+    command_connection = CommandConnection(debug=True)
+    command_connection.connect()
+
+    try:
+        res = command_connection.perform_command(evaluate_expression( channel, meta_var ))
+        result = res.result
+        print(f"Evaluated expression: {result}")
+    finally:
+        command_connection.close()
+
+    return result
+
 
 def start_intercept():
     filters = ["M1234", "M5678", "M7722"]
@@ -50,10 +69,27 @@ def start_intercept():
                 # Exit this example
                 return
             elif cde.type == CodeType.MCode and cde.majorNumber == 7722:
+                if cde.parameter("S") is None :
+                    # if there isnt an S parameter set minutes to 1
+                    minutes = "1"
+                elif cde.parameter("S").is_expression :
+                    # if there is an S parameter and it is an expression 
+                    # resolve the expression and set minutes equal to it
+                    minutes = eval_expr( cde.parameter("S").string_value, cde.channel )
+                else :
+                    # if there is an S parameter and it isnt an expression
+                    # set minutes to it
+                    minutes = cde.parameter("S").string_value
+
+                # add a + to the beginning of minutes
+                min_plus = "+" + str(minutes)
+
                 # We are going to shut down the SBC in one minute
-                subprocess.run(["sudo", "shutdown", "+1"])
+                subprocess.run(["sudo", "shutdown", min_plus])
+
                 # Resolve it with a custom response message text
-                intercept_connection.resolve_code(MessageType.Warn, "Shutting down SBC in 1min...")
+                warn_msg = "Shutting down SBC in " + str(minutes) + "min..."
+                intercept_connection.resolve_code(MessageType.Warning, warn_msg)
             else:
                 # We did not handle it so we ignore it and it will be continued to be processed
                 intercept_connection.ignore_code()
diff --git a/src/dsf/commands/code_parameter.py b/src/dsf/commands/code_parameter.py
index 24c95ed..88cd937 100644
--- a/src/dsf/commands/code_parameter.py
+++ b/src/dsf/commands/code_parameter.py
@@ -41,7 +41,7 @@ def __init__(self, letter: str, value, isString: bool = None, isDriverId: bool =
             self.letter = letter
             self.string_value = str(value)
             self.__parsed_value = value
-            self.is_expression = self.string_value.startswith("{}") and self.string_value.endswith("}")
+            self.is_expression = self.string_value.startswith("{") and self.string_value.endswith("}")
             return
 
         self.letter = letter
@@ -60,7 +60,7 @@ def __init__(self, letter: str, value, isString: bool = None, isDriverId: bool =
         # Empty parameters are represented as integers with the value 0 (e.g. G92 XY => G92 X0 Y0)
         if not value:
             self.__parsed_value = 0
-        elif value.startswith("{}") and value.endswith("}"):  # It is an expression
+        elif value.startswith("{") and value.endswith("}"):  # It is an expression
             self.is_expression = True
             self.__parsed_value = value
         elif ":" in value:  # It is an array (or a string)