The number of structures is defined by the number of Data Category 2's where the structural, hydrodynamic and hydrostatic model is input, e.g. if the user inputs two data categories (Data Categories 2.1 and 2.2), the number of structures will have been defined as 2. However, as the program is unable to anticipate that Data Category 2.3 will not be input, the Data Category 2 series must be terminated with a 'FINI' data record, that is, a data record formatted as above with 'FINI' (FINIsh) as the data category keyword. However, if the maximum number (50) of structures is input, the 'FINI' data record must be omitted, as termination of the data category series is then mandatory.