What type of icon denotes the Principal Problem in a chart?

A blue diamond is commonly used to denote the Principal Problem in data visualization and charting contexts. This convention helps to clearly identify the main issue or challenge being addressed within the data or analysis presented in the chart. The use of a distinct shape with a specific color, such as blue, serves to draw attention to the Principal Problem, making it easier for viewers to quickly recognize and understand the focal point of the analysis.

This visual cue is especially useful in complex charts where multiple elements may be present, as it provides a clear and immediate reference for identifying critical points within the data. The choice of a diamond shape also adds a geometric clarity that helps set it apart from other symbols that may represent different types of data or information.