 With Beckman's model D, later known as the DU spectrophotometer, National Technical Laboratories successfully provided the first easy-to-use single instrument containing both the optical and electronic components needed for ultraviolet-absorption spectrophotometry.The user could insert a sample, dial up the desired wavelength of light, and read the amount of absorption of that frequency from a simple meter.It produced accurate absorption spectra in both the ultraviolet and the visible regions of the spectrum with relative ease and repeatable accuracy.