Measurement calibration in the Unified Viewer allows users to set custom scales on web for PDF files across the Document Management, Drawings(Beta), Documents, and Specifications tools. If a document lacks a scale bar or legend, select any measurement tool, click Calibrate in the Scale modal, drag your cursor across a known distance on the document, and enter its real-world measurement value. You can also choose from preset scales and adjust precision levels before creating measurement markups.