Before you can define element properties, you must also define the periods to be used in the model. Periods and period levels are required to determine at what time the element should perform measurements. Period levels refer to the length of individual periods, for example, a week, month, or a year. Periods must always belong to a period level.
You can define greater periods levels for sub-elements than selected to the parent element. This way you can monitor elements, which have greater period level i.e. Year and are examined more often i.e. monthly. When the sub-element has greater period level and the parent element refers to a previous period, the period level of the element of which the values are taken is used.
Note: When defining periods, it is important that periods within the same period level do not overlap and that they do not have gaps between them, otherwise the program will always display an error message and you need to correct the situation before you can continue.