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Sometimes you would like to make SPRT measurements but traditional SPRTs are too long or awkward for a particular application. Now Hart makes a miniature glass capsule SPRT, which is perfect for cryogenics, calorimetry, and other metrology work requiring small SPRTs. The 5686 is a true SPRT. The high-purity platinum wire is hand-wound on a glass cross frame in a strain-free design. The glass capsule is designed to match the thermal expansion of the platinum wire to ensure a true seal at all operating temperatures. The capsules are pressure sealed and come protected in their own maple case. The 5686 complies completely with ITS-90 and has the following resistance ratios: W(302.9146K) 1.11807 and W(234.3156K) 0.844235. The 5686 covers temperatures from -260°C to 232°C, so it's perfect for cryogenic applications. It is 5.8 mm in diameter and 56 mm long. Fixed-point calibrations in Hart's laboratory are available for the Model 5686 which be calibrated from -200°C to 232°C. These SPRTs are small but meet customary SPRT performance for reproducibility, reliability, and stability. They solve many of the problems associated with taking precision measurements in situations unsuitable for traditional-length SPRTs. These are excellent calibration instruments.