Useful in cave survey to define the beginning of the cave. A plot of the shape and details of a cave in an intersecting plane, called the section plane which is usually vertical. The trace or outline of the details to be mapped representing their intersection with a chosen section plane. The difference in heigth between a point and a fixed level, such as mean sea level. An error is the sum of accidental and systematic errors.
Gross errors are also possible.
A typical caving cause of accidental errors is a trembling hand during bearing measurement. The amount of accidental error in a measurement can be estimated, on the basis of the measurement instrument and conditions. The measurement has no more statistical relationship with the actual value. An error that repeats itself on each measurement of the same value with the same instrument . Systematic errors can be estimated and adjusted through a proper calibration .