function drawRandomUnitWinner() public {
        require(msg.sender == owner);
        require(unitRaffleEndTime < block.timestamp);
        require(!unitRaffleWinningTicketSelected);
        
        uint256 seed = unitRaffleTicketsBought + block.timestamp;
        unitRaffleTicketThatWon = addmod(uint256(block.blockhash(block.number-1)), seed, unitRaffleTicketsBought);
        unitRaffleWinningTicketSelected = true;
    }