Generally,there are 15 factors for bimetal thermometer 1.Case: Sturdy, corrosion resistant series 304 SS case and bezel. Designed and constructed to provide a hermetic seal (IP65, NEMA 4X) which prevents crystal fogging and damage caused by moisture to the working components. Install thermometer so the maximum temperature case is kept below 200°F at all times. 2.Dial: Anti-parallax heavy gauge aluminum with white matte finish to reduce glare. Dished form with Celsius on lower inner plane and Fahrenheit on raised outer plane offers accurate indication of both scales (if equipped with dual scales). 3.External Reset: (comes standard on all process grade bimetal thermometers) A slotted-hex adjustment head offers screwdriver or wrench use to field calibrate the thermometer. This feature allows maximum accuracy at a selected area of temperature range. O-ring gasket prevents leakage and maintains weather tight seal. 4.Note: use well-agitated bath and accurate test thermometer when making any adjustment. 5.Standards: WIKA manufactures ASME B40.3 bimetal thermometers, which meet or exceed the standard issued by the American Society of Mechanical Engineers. 6.Window: Optically clear, strong glass, gasketed to maintain weather tight integrity. Acrylic and Lexan windows are available as an option but not recommended for case temperature exceeding 200°F maximum (150°F for plastic/acrylic window). 7.Pointer: Balanced, lightweight aluminum with matte black finish. 8.Stem: 304 SS welded at tip and case connector to prevent leakage. ¼" diameter is standard, 3/8" is available. Stem lengths to 72" are available, as well as 316 SS stem and connector assemblies. 9.Immersion: For accurate temperature readings, immerse the stem a minimum of 2" in agitated liquid or 4" in moving air or gas. 10.Over Range: Temporary over or under range of 50% of scale up to 500°F or 260°C will not affect the instrument's accuracy. 11.Bimetal Element: An extremely responsive temperature sensing helix which has been carefully sized and tested, heat treated and aged to relieve inherent stresses and ensure continued accuracy. 12.Accuracy: Guaranteed to be accurate to within 1% of full scale (Grade A per ASME B40.3). Calibration is to standards traceable to the National Institute of Standards and Technology. 13.Hermetic Seal: Hermetically sealed per ASME B40.3. Guaranteed not to fog up (IP65, NEMA 4X). 14.Dampening: Inert gel to minimize pointer oscillation. 15.7-Year Warranty: WIKA extends a 7-year warranty on standard types 30, 31, 50, 51, 32 and 52. Such units are guaranteed to be free from defects in material and workmanship under normal use and service. For all other  models, WIKA extends a 1-year warranty. Complete details available upon request. Filled Thermometer Policy: Silicone filling is available on selected types for ranges between -40°F and 500°F. WIKA does not recommend use of filled instruments for continual use at operating temperatures above of 400°F (204°C) or below -100° F(-70° C). Under no circumstances will an instrument warranty apply or will WIKA assume any liability for use above hese temperatures.   Per ASME B40.3, plain glass windows must not be used on filled thermometers due to expansion of fill fluid and potential lens breakage. Note: for stem lengths over 24"- consult factory