When reading a blueprint, what should you refer to if you encounter an unrecognized symbol?

When encountering an unrecognized symbol on a blueprint, consulting the legend is essential. The legend serves as a key or guide that provides definitions and explanations for symbols used in the document. Every blueprint contains various symbols that may represent different materials, fixtures, or processes relevant to the project. The legend clarifies these symbols, ensuring that anyone reading the blueprint can accurately interpret the drawings without confusion.

The scale, title block, and revision history provide important information about the dimensions, project details, and changes made to the drawing, respectively, but they do not serve to define the symbols used in the blueprint. Therefore, the legend is the correct resource to resolve any uncertainties related to symbols, making it the most appropriate answer in this context.