The parameter edit fields in HSMWorks are a bit more intelligent than the average edit field. As you change a value - using the keyboard, mouse or scroll wheel - HSMWorks evaluates the value, and changes the appearance of the field to indicate errors or warnings.
In case of an error, the field background is changed to red, and a red cross placed beside the field. If a field is indicating an error, bringing up the tooltip will show additional information about what is causing the error. In the example below, the user specified a negative Optimal Load: