When you survey a cave there are always some errors in the measurements. Most of the time, these errors are small and random. Occasionally, errors occur which are due to major mistakes in the surveying process. For example, you might read the wrong end of the compass needle or write down the wrong numbers in the survey book. These kinds of errors are called blunders.
Blunders are fairly common occurances in cave surveying.
For example, in caves like Wind and Lechuguilla, there is one blunder for every 40 to 80 shots. As a result, blunders are a big problem in cave surveying. In addition, the compiler can pinpoint the individaul shots and measurements that have caused the blunder. The program does this by first locating loops with large errors. After it finds loops with large errors, the program makes a test adjustment of each shot in the loop trying to fix the error.