This problem you are being told that the mistake is in a distance of one of the lines. But a lot of data is missing in the result's of the field data. The interior angles do add up to 720. (n - 2) x 180 degree's
The line BC is most probably the error.
Plot your work points a through f and back to a which we call a'
Take a join(inverse) a to a' and compare the direction to your traverse
Mine came close to BC direction but I didn't…"
"When viewing the stereopair of images if the overlapped portion of either images are outwards then the features will look just opposite eg; valley looks like hills and vice versa. That is pseudoscopy"