Scientists calibrated a humidity sensor used in weather balloons by testing it in conditions similar to those found in the upper atmosphere. They found that the sensor gives lower humidity readings as temperatures drop, with a significant difference at -70°C. However, the sensor was not affected much by low pressure. The calibration process showed that the sensor's accuracy is within 3.8% at a confidence level of 95%. This calibration method will help ensure accurate humidity measurements in the upper atmosphere.