The instruments using a feedback system can use calibration lines to calibrate directly the feedback force if the range of the first ones does not exceed the range of the second one. This type of gravimeter is the best one to measure the gravity values along a calibration line. It is generally used for intercomparisons with tidal instruments during a few days to calibrate them. The equivalent force was scaled against gravity by the maker. The precision of the method is poor as it is necessary to tilt the instrument in order to put and remove the ball.
Direct calibration is possible only through methods and .
During the transfer process, two kinds of errors could exist which are systematic or random. The first kind defined as systematic, is directly affecting the scale factor. This error is constant independently of the number of calibrations. The second kind which is defined like a random noise, is limiting the precision of the calibration. This kind of error decreases with the increase of the number of determinations.