Using DownloadFile()

I want to use IFTPConnection::DownloadFile(Sourcefile, DestinationFile, nStartPosLo, nStartPosHi) function to restart an incomplete transfer of file from a specific position, but not sure how to use nStartPosLo, nStartPosHi to start an incomplete transfer of file with DownloadFile function of IFTPConnection interface. As the help doesn't specifies in detail about these two parameters.
Any help would be appreciated

using SmartFTP ver. 1.5.2.3

Thanks, It works now.