170 
Process: 
2. Monitoring and execution of the voyage 
Name 
Date 
Created: 
Mathes 
26.2.98 
Data flow: 
State variables 
Checked: 
1. Origin 
• The source of state variables must be known; in the case of derived variables, this 
includes the state variables used as a basis. 
2. Validity 
• The validity of state variables must be checked from the particular sources. The test result must 
be made available to processing procedures. 
• In the case of derived state variables, the validity of the underlying variables must likewise 
be taken into account and relayed. 
3. Quality 
• Parameters which influence the quality of state variables must be transmitted (e.g. number of 
satellites in the case of satellite-assisted position determination). 
• The accuracy of state variables must be made available to processing procedures. 
• The age and frequency of updating of state variables must be known; the frequency of updating 
must be in appropriate proportion to the time constants of the process. 
• State variables must be checked for plausibility by comparison with independent sources. The 
result of the check must be provided; this requirement applies in particular to the monitoring of 
the plausibility of position and speed by way of comparison with data from a 
second independent measuring method. 
4. Harmonisation 
• The reference systems underlying the particular state variable must be known. This applies par 
ticularly to the measurement reference (e.g. ground/water-related measured variables), the 
measuring point on the ship and the geodetic datum underlying a position determination. 
• The processing or interlinking of data is permitted only where the reference systems are identical. 
This applies in particular to plausibility checks and set/actual comparisons. 
• State variables which are linked with one another are likewise to be harmonised with 
regard to their accuracy. 
5. Criticality 
• If different state variables of the same type are available, mechanisms for selection or 
prioritisation should be provided. 
6. Limit values and alarm facilities 
Messages or alarms must be provided for the following statuses: 
• loss of validity 
• change in source for a state variable type 
• change in the reference system 
• changes in the data quality (accuracy, topicality, plausibility) 
• exceeding of set/actual deviations