# Accuracy Expectations

For an Omnitrack system that includes a Mk III ROVLe system, you can expect typical position accuracy of the ROV to be the error-propagation sum of several main uncorrelated errors.

* GNSS position error, dependent on how well the user follows our guidance to keep the system out of a GNSS shadow, typically 3 to 5 meters circular-error-probable (CEP).
* GNSS compass error, also dependent on how well the user follows our guidance to keep the system out of a GNSS shadow, typically 0.5 degrees probable.
* Angular resolution from the topside unit to the deepside unit, typically 2 degrees, assuming the user has enabled the ability to use the ROV's estimate of its own depth (as we recommend). This error (in meters) is thus approximately **sin(2 degrees) \* slant range (in meters)** probable.
* Since the two angular errors are uncorrelated, the combined angular error is about 2.1 degrees probable.
* Another error, slant range measurement \[direct, straight distance between topside unit and deepside unit], is usually insignificant compared to the other errors.
* Not taking into account any other minor error sources, the system CEP is then approximately:\
   **square\_root( 25 + ( sine( 2.1 degrees ) \* slant range in meters) ^ 2 )**
* It follows that the closer the deepside unit is to the topside unit, the lower the system CEP, with the lower bound set by the GNSS position accuracy.


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