Guralp Systems Scream - Manual (Page 75)

User guide
you are using several sources. Unless the field turns red, the value is
what Scream! expected.
Block Size : The size, in bytes, of the GCF block following, not
including transport information.
The remaining fields constitute the information available from the
GCF block's internal header and mostly duplicate the information
available in the stream list. The following additional information is
available:
Decimation Index : A reserved field in older implementations of the
GCF format. Newer digitisers use this byte to provide information
about the filter-chain configuration of the digitiser, among other
things. When the byte is non-zero, Scream! will interpret it if it can,
and display the corresponding filter set-up. Refer to the Güralp
Systems technical notes (available on the web site) for more details.
Sample Rate and Compression : The current sample rate and
compression code, also displayed in Scream!'s main window.
Number of Records : GCF blocks are divided into 4-byte records. Each
record can contain 1, 2 or 4 samples, depending on the current
compression factor. Since all GCF blocks are 1024 bytes long,
allowing for the 24-byte header, a full GCF block should always
contain 250 records. However, it is permissible for a GCF block to be
only partially full.
RIC / Calculated : The Reverse Integrating Constant (effectively the
value of the last sample in the block) and its calculated value from the
differences in the block.
Checksum / Calculated : Received and calculated checksum values for
the data in the block. If these differ, Scream! assumes the data are
corrupt and asks the digitiser to re-transmit the corrupt block. If you
are using a simplex communications link, this will fail and the data
block will be lost.
Scream! also logs any errors it detects. For more information on
Scream!'s logging system, see Chapter 11 on page 126.
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