In the normal passage of a logging tool up a borehole it rotates, generating tool spin, which can be observed through the change in pad 1 azimuth. Typical rates of tool rotation are in the region of one rotation every 30 m. If an imaging or dipmeter tool completes one revolution more than every 10 m, the orientation data, and hence derived dip information, may be compromised; rotations every 2 m or less will be suspect. Rapid tool spin often occurs when a tool enters a zone of washout or leaves a section of borehole breakout. The lack of tool spin indicates that the tool is locked into one orientation; this is often due to borehole ovalisation and is an important factor in the detection of borehole breakout. Detected by observation of P1AZ curve.
See also pad-one azimuth, ovalised hole and borehole breakout.