Random Errors

Random errors are generally small errors that occur during the process of surveying. They result from the fact that it is impossible to get absolutely perfect measurements each time you read a compass, inclinometer or tape measure. For example, your hand may shake as you read the compass, the air temperature may affect the length of the tape, and you may not aim the inclinometer precisely at the target. There are literally hundreds of small variations that can affect your measurements. In addition, the instruments themselves have limitations as to how accurately they can be read. For example, most compasses don't have line markings smaller than .5 degrees. This means that the actual angle may be 123.4 degrees, but it gets written down as 123.5.

All these effects that add up to a small, random variation in measurements of survey shots. Even though these errors are random, they tend to follow a pattern. The pattern is called a "normal" distribution and it has the familiar "bell" shaped curve. As a result of this pattern, we can predict how much error there should be in a survey loop if the errors are the result of small random differences in the measurements. If a survey exceeds the predicted level of error, then the survey must have another, more profound kind of error.