diff --git a/src/NmeaParser/BufferedStreamDevice.cs b/src/NmeaParser/BufferedStreamDevice.cs
index 27fb3d6..b9dfdbb 100644
--- a/src/NmeaParser/BufferedStreamDevice.cs
+++ b/src/NmeaParser/BufferedStreamDevice.cs
@@ -29,8 +29,9 @@ namespace NmeaParser
 	/// </summary>
 	public abstract class BufferedStreamDevice : NmeaDevice
 	{
-		BufferedStream m_stream;
-		int m_readSpeed;
+		private BufferedStream m_stream;
+		private readonly int m_readSpeed;
+
 		/// <summary>
 		/// Initializes a new instance of the <see cref="BufferedStreamDevice"/> class.
 		/// </summary>
@@ -80,10 +81,10 @@ namespace NmeaParser
 		// in lastLineRead by lastLineRead at a steady stream
 		private class BufferedStream : Stream
 		{
-			private StreamReader m_sr;
+			private readonly StreamReader m_sr;
 			private byte[] m_buffer = new byte[0];
-			private System.Threading.Timer m_timer;
-			private object lockObj = new object();
+			private readonly System.Threading.Timer m_timer;
+			private readonly object lockObj = new object();
 			private string groupToken = null;
 			private string lastLineRead = null;
 			/// <summary>
diff --git a/src/NmeaParser/Nmea/Glonass/Glzda.cs b/src/NmeaParser/Nmea/Glonass/Glzda.cs
index ba39b88..e1b5be3 100644
--- a/src/NmeaParser/Nmea/Glonass/Glzda.cs
+++ b/src/NmeaParser/Nmea/Glonass/Glzda.cs
@@ -1,5 +1,8 @@
 namespace NmeaParser.Nmea.Glonass
 {
+    /// <summary>
+    /// Date and time of fix
+    /// </summary>
     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1704:IdentifiersShouldBeSpelledCorrectly", MessageId = "Glzda")]
     [NmeaMessageType("GLZDA")]
     public class Glzda : Zda
diff --git a/src/NmeaParser/Nmea/Gnss/Gnzda.cs b/src/NmeaParser/Nmea/Gnss/Gnzda.cs
index fd9ab6b..15f4198 100644
--- a/src/NmeaParser/Nmea/Gnss/Gnzda.cs
+++ b/src/NmeaParser/Nmea/Gnss/Gnzda.cs
@@ -1,5 +1,8 @@
 namespace NmeaParser.Nmea.Gnss
 {
+    /// <summary>
+    /// Date and time of fix
+    /// </summary>
     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1704:IdentifiersShouldBeSpelledCorrectly", MessageId = "Gnzda")]
     [NmeaMessageType("GNZDA")]
     public class Gnzda : Zda
diff --git a/src/NmeaParser/Nmea/Gps/GPZDA.cs b/src/NmeaParser/Nmea/Gps/GPZDA.cs
index 0574cff..28744dd 100644
--- a/src/NmeaParser/Nmea/Gps/GPZDA.cs
+++ b/src/NmeaParser/Nmea/Gps/GPZDA.cs
@@ -1,5 +1,8 @@
 namespace NmeaParser.Nmea.Gps
 {
+    /// <summary>
+    /// Date and time of fix
+    /// </summary>
     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1704:IdentifiersShouldBeSpelledCorrectly", MessageId = "Gpzda")]
     [NmeaMessageType("GPZDA")]
     public class Gpzda : Zda
diff --git a/src/NmeaParser/Nmea/NmeaMessage.cs b/src/NmeaParser/Nmea/NmeaMessage.cs
index 779da33..39550b3 100644
--- a/src/NmeaParser/Nmea/NmeaMessage.cs
+++ b/src/NmeaParser/Nmea/NmeaMessage.cs
@@ -49,7 +49,7 @@ namespace NmeaParser.Nmea
 	/// </summary>
 	public abstract class NmeaMessage
 	{
-        private static Dictionary<string, ConstructorInfo> messageTypes;
+        private readonly static Dictionary<string, ConstructorInfo> messageTypes;
 
         /// <summary>
         /// Initializes an instance of the NMEA message
@@ -199,8 +199,7 @@ namespace NmeaParser.Nmea
 
 		internal static double StringToDouble(string value)
 		{
-			double result = double.NaN;
-			if(value != null && double.TryParse(value, NumberStyles.Any, CultureInfo.InvariantCulture, out result))
+			if(value != null && double.TryParse(value, NumberStyles.Any, CultureInfo.InvariantCulture, out double result))
 			{
 				return result;
 			}
diff --git a/src/NmeaParser/NmeaDevice.cs b/src/NmeaParser/NmeaDevice.cs
index 52287e4..2a37776 100644
--- a/src/NmeaParser/NmeaDevice.cs
+++ b/src/NmeaParser/NmeaDevice.cs
@@ -29,7 +29,7 @@ namespace NmeaParser
 	/// </summary>
 	public abstract class NmeaDevice : IDisposable
 	{
-		private object m_lockObject = new object();
+		private readonly object m_lockObject = new object();
 		private string m_message = "";
 		private Stream m_stream;
 		private CancellationTokenSource m_cts;
diff --git a/src/NmeaParser/StreamDevice.cs b/src/NmeaParser/StreamDevice.cs
index 96c34cc..7d55f05 100644
--- a/src/NmeaParser/StreamDevice.cs
+++ b/src/NmeaParser/StreamDevice.cs
@@ -27,7 +27,8 @@ namespace NmeaParser
 	/// </summary>
     public class StreamDevice : NmeaDevice
     {
-		System.IO.Stream m_stream;
+		private Stream m_stream;
+
 		/// <summary>
 		/// Initializes a new instance of the <see cref="StreamDevice"/> class.
 		/// </summary>