English: a solution of 4% holmium oxide in 10% perchloric acid, permanently fused into a 1 cm pathlength quartz cuvette. The wavelength values of the transmittance minimum of 14 absorption bands is certified to a wavelength uncertainty of about 0.2 nm, with the actual uncertainty varying with the band and the instrumental spectral bandwidth. The standard is certified for spectral bandwidths from 0.1 nm to 3.0 nm, and for wavelengths from 240 nm to 650 nm.