# Bias

Bias is the difference between the observed average of measurements and the reference value or true value of the part.

To determine the measurement system’s BIAS at a specific location in the process range, it is necessary to obtain accurate reference value of a part. This can usually be done with tool room or layout inspection equipment.

Measure one of the sample parts precisely on tool room or layout inspection equipment

Have one appraiser measure the same part a minimum of 5 times, using the gauge being evaluated.

Calculate the average of the readings. The difference between the reference value and the observed average represents the measurement system’s bias

If an index is desired, convert bias to a percentage of process variation (or tolerance), by multiplying 100 and dividing by the process variation (or tolerance).

Study to find Bias is divided into three parts - Bias Mapping, Bias Measurement and Bias Data Analysis.