startingBlock property
The field represents the index of the block used in the synchronisation currently in progress. startingBlock is the block at which the sync started, currentBlock is the block that is currently processed and finalBlock is an estimate of the highest block number this synchronisation will contain. When the client is not syncing at the moment, these fields will be null and isSyncing will be false.
Implementation
final int? startingBlock, currentBlock, finalBlock;