The Foreshot/Backshot dialog requires you to enter the Foreshot to Next Station and the Backshot from Next Station. Although this is not the order in which shots are recorded in the field, entering the shots this way will make it obvious to you whether the bearings are 180 degrees apart and therefore, whether they are accurate.
Note: the Backshot from Next Station is measured in the same sense as the Foreshot e.g. if the Foreshot was 0 this angle should be approximately 180. You can also enter the backshot adjusted by 180 degrees in the Adjusted by 180 degrees field. This angle should be approximately the same angle as the foreshot. The Difference indicates the measurement error.
If Absolute Azimuths is enabled and Calculate Azimuth using Turning Angle and Last Azimuth is disabled, the foreshot and backshot are averaged to determine the azimuth towards the next station.
If you enable Calculate Azimuth using Turning Angle and Last Azimuth, the angular change between the foreshot to the next station and the backshot to the previous station is added to the previous direction to determine the bearing towards the next station.
If you return to the calculation of stations by absolute azimuth after a series of uninterrupted turning angles the final bearing of the turning angle segment will be compared to the first absolute azimuth (first foreshot of the next segment of traverse having absolute azimuths). If these two bearings differ, the last bearing of the turning angle segment is forced to equal the first bearing of the absolute azimuth segment and the angular difference is allocated evenly backwards throughout the turning angle segment. Note that you can identify which segments are turning angle segments because the station column will have a "~" for stations with the Calculate azimuth using turning angle and last azimuth option enabled.
