GB/T 26813-2011 "Double Beam UV-Visible Spectrophotometer" applies to double-beam UV-visible spectrophotometers with independent reference beams and reference sample cells, covering a spectral range of 200 nm to 900 nm with continuous wavelength adjustment. Similar instruments within comparable wavelength ranges may also refer to this standard. It specifies instrument classification, technical requirements, test methods, inspection rules, as well as marking, packaging, transportation, and storage. The standard divides instruments into three grades, clarifying indicators such as wavelength accuracy, repeatability, spectral bandwidth, transmittance accuracy, and repeatability for each grade. It standardizes test conditions and operational procedures, providing unified technical guidelines for instrument production, inspection, and use to ensure the accuracy and consistency of measurement results.