A double down lets you double your bet in exchange for one final card. You need to set the amount of money that you aim to win while scratching cards.
https://www.ww2.site/forum/viewtopic.php?p=262139#p262139
http://forum3.bandingklub.cz/viewtopic.php?f=21&t=1309853
http://www.prepody.ru/topic69264.html
http://sharecovid19story.com/viewtopic.php?t=2695739
https://debate.socialism.nl/forum/showthread.php?tid=155763
https://debate.socialism.nl/forum/showthread.php?tid=103657
https://debate.socialism.nl/forum/showthread.php?tid=179765
http://users.atw.hu/tunedthings/viewtopic.php?p=337069#337069
http://www.horsecity.ru/phpBB3/viewtopic.php?f=13&t=247931
https://debate.socialism.nl/forum/showthread.php?tid=152875
https://www.clubhombre.com/mybb/showthread.php?tid=15527
https://ebagcilar.com/forum/index.php?topic=14446.msg135017#msg135017