A measurement system for measuring a degree of moisture stratification in a flat sheet product, such as paper, board or other materials. The system uses a combination of a reflection gauge and a transmission gauge to provide output signals indicative of surface moisture of a first side and of moisture in the body of the flat sheet product. The output signals are processed by a controller or computer to provide a measurement of the moisture stratification. An additional reflection gauge and an additional transmission gauge can also be used to provide additional output signals indicative of surface moisture of a second side of the flat sheet product and of moisture in the body. Narrow band radiation is used with modulation to distinguish from ambient radiation as well as radiation incident on the opposite side.