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There are many sources of noise which affects IMUs. The Allan Variance plot is designed to help engineers estimate 5 different noise parameters for each axis of both the gyroscope and accelerometer. We primarily focus on only two: White Noise and Random Walk but

IMU noise parameter	Variable	Note
Quantization noise	Q
White Noise	N	Often referred to as Angle Random Walk (For Gyros) and sometimes Velocity Random Walk (For accelerometers.) This is because when white noise is integrated it results in a random walk.
Bias Instability	B	This is often incorrectly used as the sigma for changing bias. The reason is either because of a mistake (the name is misleading) or because it is in fact a good approximation of the correct parameter and is easier to calculate.
Random Walk	K	This is the correct variable for the sigma of the randomly changing bias
Ramp error	R

See also:

• Units