The spaceborne Argos instrument receives messages for the time corresponding to the message length, that is, the number of blocks indicated at the start of the message. If a transmitter indicates that a message contains more blocks than it has actually sent, the instrument receives noise in the form of random zero-bits or one-bits until the end of the message is reached.

Argos processing centers process telemetry from the satellites. The sensor fields in the messages are processed and transfer functions are declared in the User Office (BUT) database. As a general rule, the declared length of the sensor field and the actual length of the message received by the Argos instrument are the same, but variations do occur.

1. If the sensor field in the message received is the same length or shorter than the value specified in the BUT database, all bits received are processed. In other words, the system does not substitute values for "missing" bits.
   Example: A message is declared in the BUT database as containing 16 8-bit sensor fields (128 bits in total); the satellite receives a message indicating a sensor field length of 96 bits. Consequently, only the first 96 bits are processed and distributed.
2. If the sensor field in the message is longer than the declared BUT value, it is processed in two ways:
   a) "Priority to received message": The values in the sensor field are processed in full, even if processing of the additional bits is not specified in the BUT database. Additional sensor values are processed by default in blocks of 8 bits and distributed in hexadecimal.
   b) "Priority to BUT declarations": The values in the sensor field must be processed exactly as specified in the BUT database and additional bits are not distributed.

Priority is currently given to received messages. From 1 October 2002, BUT declarations will take priority.
Example: A message is declared in the BUT database as containing six 8-bit sensor values to be distributed in hexadecimal (declared values do not have to be multiples of 32 bits). The received message contains two blocks of 32 bits. Consequently, only the first 48 bits are processed and distributed.

This change makes it possible to distribute sensor values from transmitters with 28-bit ID numbers (32767 and above) in the same way as transmitters with 20-bit ID numbers.

We recommend that you check your BUT declarations now to make sure that they match the type of message sent by your transmitters.