the unit features a blue-green, light-emitting vacuum fluorescent display (vfd). the display device itself has 9 seven segment digits, 8 of which are used for numeric output, the 9th being for the minus sign or to accommodate a space for 6+2 scientific notation. although only capable of displaying 6 figures when using scientific notation, the calculator works internally to 8. a vacuum fluorescent display (vfd) is a display device used commonly on consumer-electronics equipment such as video cassette recorders, car radios, and microwave ovens. a vfd operates on the principle of cathodoluminescence, roughly similar to a cathode ray tube, but operating at much lower voltages.