<#285#>When a new model is started, the nominal segment length must be specified before any major elements can be entered<#285#>. Experience has taught many new users have problems with the code at this initial stage, not realizing that a nominal segment length is <#286#>required<#286#>. Any reasonable value suffices; as already discussed the nominal segment length can be changes at any time during the modelling process. The first major element can then be entered. If a model is already loaded, and the user wants to start a new model, it is easiest to quit and run the program again.