making of scientific instruments. The company rented larger quarters at 3330 Colorado Street, and began manufacturing pH meters. The pH meter is an important device for measuring the pH of a solution, and by 11 May 1939, sales were successful enough that Beckman left Caltech to become the full-time president of National Technical Laboratories. By 1940, Beckman was able to take out a loan to build his own 12,000 square foot factory in South Pasadena. Spectrophotometry Ultraviolet In 1940, the equipment needed to measure light energy in the visible spectrum could cost a laboratory as much as $3,000, a huge amount at that time. There was also growing interest in examining ultraviolet spectra beyond that range. Just as Beckman had created a single easy-to-use instrument for measuring pH, he made it a goal to create an easy-to-use instrument for spectrophotometry. Beckman's research team, led by Howard Cary, developed several models. The new spectrophotometers used a prism to separate light into its absorption spectrum and a phototube to electrically measure the light energy across the spectrum. They allowed the user to plot the light absorption spectrum of a substance, giving a standardized "fingerprint", characteristic of a compound. 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. The National Bureau of Standards ran tests to certify that the DU's results were accurate and repeatable and recommended its use. Beckman's DU spectrophotometer has been referred to as the "model T" of scientific instruments: "This device forever simplified and streamlined chemical analysis, by allowing researchers to perform a 99.9% accurate quantitative measurement of a substance within minutes, as opposed to the weeks required previously for results of only 25% accuracy." Theodore L. Brown notes that it "revolutionized the measurement of light signals from samples". Nobel laureate Bruce Merrifield is quoted as calling the DU spectrophotometer "probably the most important instrument ever developed towards the advancement of bioscience." Development of the spectrophotometer also had direct relevance to the war effort. For example, the role of