MwD

The MWD (Measurement While Drilling) system was developed to collect measurements during drilling and send information to the surface. It was first used in the 1970s. Previously, wireline logging required stopping the drilling, removing the drill pipe, and using wireline tools to retrieve survey data. The MWD tool, however, transmitted survey readings through the mud stream in the drill pipe, saving time compared to wireline logging. The survey data could be transmitted through the mud stream or using electromagnetic and acoustic methods. Initially, the MWD system provided three key measurements: inclination, azimuth, and toolface. These measurements helped the directional driller position the well accurately.

MWD tools can also provide information about the conditions at the drill bit. This may include:
Rotational speed of the drillstring
Smoothness of that rotation
Type and severity of any vibration downhole
Downhole temperature
Torque and Weight on Bit, measured near the drill bit
Mud flow volume