"The first reliable paper money identifier to aid blind business persons has been developed from NASA technology. The device identifies paper money by its sound "signature." As a bill is passed under a light source, a photo-transistor measures changes in the bill's light patterns. These changes are converted into "beeping" sounds by an oscillator. Since each denomination of paper money has a different pattern a different series of tones is given off. These differences are easily identified after only about three hours of practice. NASA technology which led to development of the device stems from a technique for the semi-automatic inspection of microfilm records first reported in 1969. The Marchak Engineering and Manufacturing Co., Austin, Tex., produces the device commercially."