National Institute of Standards and Technology (NIST) certified standard polystyrene film used for wavenumber calibration and accuracy testing of Infrared Spectrometers. Certificate of traceability for 5 NIST 1921b wavenumber values. This is a set of 2 films. Each film is mounted to 2” x 4” cardstock holder for ease of use in the cassette holder that comes standard with all Shimadzu FTIR models.