National Physical Laboratory

Eye averaging

An eye averaged reading is obtained by the operator observing a fluctuating displayed reading and manually determining the average. 

There are two main techniques to eye averaging.

  1. Systematic technique whereby the result is taken to be the mean between the minimum and maximum of the observed readings over a period of time. 

  2. Intuitive approach whereby the operator takes the perceived mean of the measurement readings over a period of time as the result.

Both techniques must be tempered with a degree of common sense to discount spurious/extreme readings.

Experiences in industry have often found the intuitive method can provide as good, if not better, results as the systematic approach - most operators tend to be very good at eliminating outliers and make a weighted average of the low versus higher readings which the systematic approach does not take into account.

It is important that the user is comfortable with the display characteristics of the instrument being used (e.g. with a log scale, the mid-point between the two marks is not the numerical mid-point value). If the pointer is not very close to the scale, care must be taken to avoid parallax errors, especially if the display is being viewed via a camera.

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