  We describe the laboratory complex for the calibration of photometers that
are used in weather service to measure the water vapor content in the Earth
atmosphere. The complex was built up in Pulkovo Observatory and developed
within the framework of collaboration between Pulkovo Observatory and
Lindenberg Meteorological Observatory (Meteorologisches Observatorium
Lindenberg - Richard-A{\ss}mann-Observatorium, Lindenberg, Germany). It is used
to obtain calibration dependences for individual devices, and also to develop
and compare various methods of construction of calibration dependences. These
techniques are based on direct calibration of the photometers, on the use of
spectral laboratory transmission functions for water vapor, on calculation
methods using spectroscopical databases for individual lines. We hope that when
the parameters of the equipment are taken into account in detail and new
results for the absorptive power of water vapor are used, the accuracy of
determination of the water vapor content in the atmosphere of 1-2% may be
attained.
