What indicates if a drawing has been modified?

The revision block or ruled columns are crucial elements on a drawing that help identify any modifications made to it. This block typically contains information regarding the revision history, including the revision number, date, and a brief description of the changes that were made. By referencing this section, anyone viewing the drawing can quickly determine if it has been altered and understand the nature of those modifications.

In contrast, while colors, line thickness, and title blocks can provide some context about a drawing, they do not specifically convey modification history. Colors may indicate different design features but do not reliably signal changes. Title blocks contain essential information about the drawing, such as the title, scale, and author, but do not track revisions. Likewise, line thickness might reflect different aspects of the drawing, but does not inherently indicate whether the drawing itself has been modified. Thus, the revision block is the definitive reference for modifications.