What is dry leg and wet leg measurement?

wet leg is filling the impulse lines of the differential pressure transmitter with a different fluid (usually heavier ) than the process fluid .
when using a differential pressure transmitter if the fluid measured can evaporate and condensate we use the wet leg measurement so that the condensate fluid doesn't affect the readings to give false indications , if the fluid can't evaporate and condensate we use the much easier to maintain and calibrate than the wet leg .

does any body still use wet leg and dry leg in level or pressure measurements :S