From RAD Studio VCL Reference
unsigned short duFurlongs;
The duFurlongs variable represents the conversion type for furlongs.
Use duFurlongs to convert from another measurement unit to furlongs.
Note: Do not change the value of duFurlongs. duFurlongs contains a handle obtained by a call to RegisterConversionType. Changing the value of duFurlongs will make distance conversions not work properly.