The UARS microwave limb sounder measures water vapor in the upper atmosphere. The researchers checked the accuracy of these measurements and compared them with other instruments. They found that the water vapor measurements are accurate to within 20-25% in the lower stratosphere and 8-13% in the upper stratosphere. The precision of a single measurement is around 0.15 parts per million by volume in the midstratosphere. In the lower mesosphere, the precision is 0.25-0.45 parts per million by volume. During polar winter, the measurements at 46 hPa can be influenced by climatology. The vertical resolution of the measurements is around 5 kilometers.