What is the difference between an individual reading in a series of observations and the mean called?

The correct term for the difference between an individual reading in a series of observations and the mean is called deviation. Deviation specifically quantifies how much a single data point differs from the average (mean) of a dataset. When conducting measurements and analyses in surveying, understanding deviations helps in assessing the accuracy and precision of the data collected.

Residual, while related to the difference between observed values and a fitted line or model, specifically pertains to model assessments in statistical regression contexts. Variance refers to the average of the squared deviations from the mean, providing a measure of how spread out the numbers are. Error margin typically describes a range of values that is expected to contain the true parameter being estimated, often associated with confidence intervals or estimation precision rather than individual observations. Thus, deviation is the most accurate term for the stated concept.