In order to speed the calculation input process and also to assist novices to the technical subject that the program addresses a number of input values are set to 'defaults'. This means that the program will 'assume' the value of the input the user wishes to enter. This system of entering defaults is only used only when it is 'safe' to do so and the user is always provided with the facility to over-ride default values. Default values may also be 'dynamic', meaning that they adjust automatically as a result of other input values the user may already have entered or subsequently edits.