A well log of the traveltime (transit time) for seismic waves per unit distance, usually measured in microseconds per foot, which is the reciprocal of the P-wave velocity. Also called acoustic-velocity log and continuous-velocity log. Usually measured with frequencies 1 to 50 kHz. Used for porosity determination by the time-average equation (q.v.). The interval transit time is integrated down the borehole to give total one-way traveltime. For the compensated sonic log, two transmitters are pulsed alternately and measurements are averaged to cancel errors due to sonde tilt or changes in hole size. See Figure S-13 and also cycle skip, dipole sonic log, array log, cement bond log, and fracture log.