Tares, or offsets, occur when the relative-gravity meter reading "jumps" during a survey; a tare affects all subsequent observations, but does not affect observations recorded prior to the tare. Tares may be added using the "Process > Add tare..." menu item, which brings up the dialog:
Here, the user may specify a date and magnitude of a tare. The tare value is simply subtracted (or added, if negative) to all relative-gravity observations within the currently-active loop that are recorded after the specified time.
The tare table, shown on the Drift tab, shows tares that have been added. More than one tare can be applied simultaneously, and tares are cumulative. That is, if a 10 µGal tare occurs one hour into a survey, and a 20 µGal tare two hours into a survey, after two hours a 30 µGal tare will be subtracted from all subsequent observations.
Tares shown in the tare table can be temporarily disabled by unchecking the respective check box. The delta-g observations shown on the Drift tab are updated immediately.
Tares may also be permanently removed by right-clicking on the tare in the Tare table and selecting "Delete tare."
The time at which a tare occurred is shown by a sold vertical line in the drift window:
Note that the tare only affects delta-g's that span the time of the tare. Repeat observations that both take place before the tare, or both after the tare, are unaffected.
