# What is the accuracy of Doppler locations?

Location accuracy varies with the geometrical conditions of the satellite passes, the stability of the transmitter oscillator, the number of messages collected and their distribution in the pass. This means in particular that a given transmitter can have locations distributed over several classes during its lifetime. Classes for which accuracy is estimated and related values:

- Class 3: better than 250 m radius
- Class 2: better than 500 m radius
- Class 1: better than 1500 m radius
- Class 0: over 1500 m radius

The error is assumed to be isotropic and hence characterized by a single number called the radius of error. It corresponds to one standard deviation (sigma) of the estimated location error. The location class is attributed based on the radius of error. The location class and associated error are sufficient for many applications.