Abstract: A measurement means for a downhole tool for determining the orientation of the axis of a downhole tool in relation to true north. It includes a gyro sensor capable of measuring angular rate, a rotation means for rotating the gyro sensor about a sensor axis, a measurement means to detect the angular rate at the gyro sensor as it is rotated to form a series of readings, and a processor capable of interpreting the signal amplitude from the series of readings and determining the points of greatest signal amplitude. The processor is also being capable of comparing the phase difference between the actual readings taken against what would be generated with the sensor pointing true north thus providing a downhole tool axis angular deviation from true north. The rotation means rotates the gyro sensor in discrete steps.

Abstract: A measurement means for a downhole tool for determining the orientation of the axis of a downhole tool in relation to true north. It includes a gyro sensor capable of measuring angular rate, a rotation means for rotating the gyro sensor about a sensor axis, a measurement means to detect the angular rate at the gyro sensor as it is rotated to form a series of readings, and a processor capable of interpreting the signal amplitude from the series of readings and determining the points of greatest signal amplitude. The processor is also being capable of comparing the phase difference between the actual readings taken against what would be generated with the sensor pointing true north thus providing a downhole tool axis angular deviation from true north. The rotation means rotates the gyro sensor in discrete steps.