features: 1.With its single beam optical path structure of low stray light, high resolution grating type, the instruments have good stability, repeatability, luminosity linearity and precise measurement readings. In addition, a narrower spectrum bandwidth is available to satisfy the need of normal analytical measuring & testing projects. 2.The use of the optimized design and the latest microprocessor technology makes the instruments have the control functions of automatic adjustment of 0%T and 100%T, etc. and also measuring & testing modes of T, A, C, F, etc. (no C, F for Type 721). 3.Its digital indicator can indicate transmittance, absorption, concentration and other parameters brightly and clearly, improving the precision of the readings of the instruments. 4.The instruments are equipped with a standard RS-232 two-way telecommunication interface (no such an interface for Type 721), which can be connected with not only a serial printer, but also a computer (that can use SPD user application software on Windows operation system), it has application functions of luminosity measuring & testing (T, A), quantitative measuring & testing (C, F), time scanning, etc. It can also be used to collect, store and access.