From ControlTheoryPro.com

Contents
1 Introduction  Angle Random Walk
If you are looking at the specificatons for a rate sensor they will most likely include a value for Angle Random Walk (ARW). ARW is a contributor, often a dominant contributor to Noise Equivalent Angle.
2 Rate Sensor Basics
A rate sensor measure the rate of rotation about is sensitive axis. The sensor output is typically a voltage which represents the rotation rate. The number of volts per (deg/s) or per (rad/s) is known as the scale factor.
2.1 Noise Sources
 Random Noise (often electrical noise)
 Thermal (this can cause scale factors to change and create electrical noise)
2.2 Errors in the signal
 Scale Factor Variation across the bandwidth
 Bias Error
 CrossAxis Angular Error
 Sensitivity (an error in the form of truncation)
3 Angular Error from a Rate Sensor
Often the rate sensor is used in order to determine an angle. This is done by integrating the rate signal over time. When integrated Angle White Noise (AWN) will wander. This wander from the integrated rate is ARW.
ARW, as specified by manufactuerers, is due to noise exclusively not errors caused by scale factor or bias mismatch. The ARW will grow the longer you integrate.
4 Conversion from PSD, FFT, and Bandwidth to ARW
5 External Links
Angle Random Walk Application Note from Crossbow
 Note there is an IEEE standard on ARW (might be 975) that should be included but I couldn't find a link on the web. Please add one if you have it. Gabe