A diagonal line of ‘heat’ from bottom left to top right reveals people choosing double digits (2323, 6868 etc). A strong horizontal line at the 19 point shows people using their birth year as a PIN code (1971, 1998 etc). And a large amount of heat in the bottom left shows how people commonly use their birthdate in a MM/DD or DD/MM format. The most common code in the set is 1234.
https://cdn.masto.host/vissocial/media_attachments/files/112/400/212/751/652/950/original/98fa39ed24befb59.png