# To measure points in two faces

You can observe points using face 1 (direct) and face 2 (reverse) measurements during a station setup and when using the Measure rounds or Measure topo measurement methods. The software creates Mean Turn Angle (MTA) records for observations to the same point, including paired face 1 and face 2 observations or grouped face 1 only observations.

When measuring points in two faces, consider the station setup method and the new point measurement method together and select the appropriate methods according to how you want to capture and store the data.

To use a single backsight (measured on one or both faces) and measure some topo points (on one or both faces), then use station setup and Measure topo. When measuring points on both faces, use Measure topo to observe the backsight on the other face. Alternatively, use Measure rounds and include the observation to the backsight point in the rounds. Otherwise, all foresights on face 2 will be oriented using the face 1 backsight observation.

- MTAs are not created during Station setup, but are created later if you make further observations to the backsight using Measure topo or Measure rounds.
- When you use Measure topo, MTAs are calculated and stored on the fly.
- Once an MTA record is written to the job database, you cannot change it. You can delete a face 1 and face 2 observation but the MTA records are not updated. You cannot delete MTA records in review.

To measure multiple backsights, multiple rounds of observations, or to obtain better quality control of your observations, complete the station setup using Station setup plus or Resection. Either method enables you to:

- measure a single backsight point or multiple backsight points
- measure backsight and foresight points
- pair the face 1 and face 2 observations and create MTA records
- measure face 1 only observations and create MTA records

- measure one or more rounds of observations

- review the quality of the observations and remove bad observations

Use Resection if you also need to determine the coordinates of the instrument point by making observations to known backsight points.

After performing the station setup, use Measure rounds to:

- measure one or more foresight points
- pair the face 1 and face 2 observations and create MTA records
- measure face 1 only observations and create MTA records
- measure one or more sets of observations per point in one round
- measure one or more rounds of observations
- review the standard deviations of the observations and remove bad observations

If the station setup has:

- a single backsight, you can choose whether or not to include the backsight point in the rounds list.
- multiple backsights, the backsight points are not included in the rounds list.

- If you do not measure the backsight on face 2, then the horizontal angle face 2 measurements that were observed using Measure rounds will not be used when calculating the MTAs.
- When you use Measure rounds after a station setup with a single backsight, and you do not include the backsight point in the rounds list, all turned angles are calculated using the backsight observation(s) made during the station setup.
- When you make topo observations after a Station setup, and you subsequently select Measure rounds, you must reobserve the backsight to include it in the rounds, generate an MTA to the backsight, and calculate turned angles from the backsight MTA for all foresight points.
- When you use Station setup plus or Resection, all observations are stored when the station setup is complete. MTAs are stored at the end. When you use Measure rounds, the observations are stored at the end of each round. In all three options, the MTAs are stored at the end.
- You can create MTAs during a station setup using Station setup plus and Resection, and also after a station setup using Measure rounds or Measure topo. When you measure the same point(s) using Measure rounds or Measure topo after Station setup plus and Resection, the software may produce two MTAs for the one point. When more than one MTA exists for the same point in one station setup, the Trimble Access software always uses the first MTA. To avoid having two MTAs for the same point, do not use both methods to measure a point.