Factory calibration is an integral step in the manufacture and repair of many LI-COR instruments. The characteristics of optical and other components change with time and may be affected by environmental conditions. Data of a critical nature may require more frequent calibrations than those suggested, as well as calibrating under conditions of actual use (e.g., same temperature). Many instruments also require user calibration to compensate for daily, or more frequent, changes in barometric pressure and/or temperature. A more extensive factory recalibration is recommended for many instruments; the recommended frequency, and what is included with the factory recalibration for each instrument can be found by selecting your instrument from light sensors, gas analyzers, photosynthesis systems, soil gas flux systems, and sensors below.