Yes, but the CG-5 automatically corrects for the static drift, as long as you let it repeating readings at the same position during around 24 hours in drift mode, before you go to the field, so as to determine the long term drift correction to be applied. However, notice that you will still have to manually calculate the dynamic drift from repeated measurements at a reference station at different times during you survey.

In the field you have to determin the drift of CG5 by repeating measurments manually.

As stated earlier CG5 automatically corrects for the sensor drift with a value obtained during the 24 hour drift calibration in a queit and stable environment. Even for one day you'll still need the drift correction value.regards

As Prof. Leite says above, there is firstly the calibration of the long-term drift to be done in advance, which is then pre-set. Secondly there is a residual drift. To estimate this, in my experience with two different CG-5s in the same survey area, you definitely should return to a local base station every 4 hours, maximum. Thirdly, there is the tidal correction set the meter, but it needs to be checked against another program. I found on the first of the two surveys carried out in successive years at the same site that my meter-applied tidal correction was 2 hours out, because the 1-hour advance in local time compared to GMT had been applied in the wrong sense. This was because the user manual is not very clear.

Regarding individual station readings, I found that the meter hired for the second survey behaved differently from that of the previous year. Over several repeated readings the raw reading on the second meter would rise, then flatten out asymptotically to a stable value.

Your network of local base stations needs also to be tied in to the master base station by repeated visits from local to master over as short a time period as possible, and calculating the residual drift between each pair local-master.

Here is a short extract from the second field report:

The maximum attainable precision of the instrument ( 0.001 mGal) is only obtainable under laboratory conditions, which are never achievable in the field. It would be necessary to have a station comprising a concrete-floored, sheltered base far from traffic noise, and also to spend half an hour or more on each reading. In addition, there is a trade-off between the time one is prepared to spend at any one station and the coverage of the survey area desired. In practice, individual stations are measurable to, say, better than about 0.01 mGal, but after drift and other effects, which cannot be entirely eliminated, the final accuracy may be no better than 0.02 mGal. Nevertheless, the resulting map should still satisfactorily define anomalies of ten times that amplitude (0.2 mGal).

In practice our survey defined useful anomalies of 0.4 to 0.5 mGal in amplitude. If you are interested in studying further this high-resolution survey, from the point of view of extracting the maximum resolution from a CG-5, I could send you the two reports of the field work and data reduction.

Working with a gap of ~8 h between the reading in the base station, you may find instrumental drift of about 1x10e-7 mGal/minute, or something like this. Thus, if it's not possible to return to your base in 4 hours, you can read just in the begining and in the finish of the day. But, of course, more readings in the base means more precision in your correction, It's up to you and the logistic of the survey.

Yes, drift correction must done all the time in gravity survey, that because we are dealing  with a natural phenomena measurements (the gravity field ), which is vary continuously with time.

• I think that the change in drift and tidal is random that needs to return to the base station more than twice during the survey and within a specific time that does not exceed one hour, especially if the study is local and needs high accuracy (engineering geophysics), as the readings in the base station must be intensified and with an interval of less than an hour.