How to calculate accuracy of latitude/longitude

I'm updating a Windows Mobile application to capture location information using the built-in GPS hardware. The Microsoft API provides a method GPSGetPosition that returns the following struct (ref:GPS_POSITION):

``````typedef struct _GPS_POSITION {
DWORD dwVersion;
DWORD dwSize;
DWORD dwValidFields;
DWORD dwFlags;
SYSTEMTIME stUTCTime;
double dblLatitude;
double dblLongitude;
float  flSpeed;
double dblMagneticVariation;
float  flAltitudeWRTSeaLevel;
float  flAltitudeWRTEllipsoid;
GPS_FIX_QUALITY     FixQuality;
GPS_FIX_TYPE        FixType;
GPS_FIX_SELECTION   SelectionType;
float flPositionDilutionOfPrecision;
float flHorizontalDilutionOfPrecision;
float flVerticalDilutionOfPrecision;
DWORD dwSatelliteCount;
DWORD rgdwSatellitesUsedPRNs[GPS_MAX_SATELLITES];
DWORD dwSatellitesInView;
DWORD rgdwSatellitesInViewPRNs[GPS_MAX_SATELLITES];
DWORD rgdwSatellitesInViewElevation[GPS_MAX_SATELLITES];
DWORD rgdwSatellitesInViewAzimuth[GPS_MAX_SATELLITES];
DWORD rgdwSatellitesInViewSignalToNoiseRatio[GPS_MAX_SATELLITES];
} GPS_POSITION, *PGPS_POSITION;
``````

So I can determine the latitude and longitude but I would like to be able to calculate the accuracy of the result. The application runs on a Trimble Juno and the GPS Controller application on the device provides an accuracy value in metres. Is this something I can determine from the values in the struct or is this something specific to the hardware that would require a native function call? Is the accuracy value based on heuristics or is it a common calculation across different hardware?