/// <summary>
        /// Calculate the percent error for the maginitude against
        /// the GPS value.
        /// </summary>
        private void CalculatePercentError()
        {
            if (GpsMag != 0)
            {
                // Mag Error
                BtEarthPercentError      = MathHelper.PercentError(GpsMag, BtEarthMag);
                BtInstrumentPercentError = MathHelper.PercentError(GpsMag, BtInstrumentMag);
                WpEarthPercentError      = MathHelper.PercentError(GpsMag, WpEarthMag);
                WpInstrumentPercentError = MathHelper.PercentError(GpsMag, WpInstrumentMag);

                // Dir Error
                //BtEarthDirError = MathHelper.PercentError(GpsDir, BtEarthDir);
                //BtInstrumentDirError = MathHelper.PercentError(GpsDir, BtInstrumentDir);
                //WpEarthDirError = MathHelper.PercentError(GpsDir, WpEarthDir);
                //WpInstrumentDirError = MathHelper.PercentError(GpsDir, WpInstrumentDir);

                // Dir Error
                BtEarthDirError      = MathHelper.AngleDiff(GpsDir, BtEarthDir);
                BtInstrumentDirError = MathHelper.AngleDiff(GpsDir, BtInstrumentDir);
                WpEarthDirError      = MathHelper.AngleDiff(GpsDir, WpEarthDir);
                WpInstrumentDirError = MathHelper.AngleDiff(GpsDir, WpInstrumentDir);
            }
        }