Arithmancy Numbers, which are the basis for divination through arithmancy. The numbers have different meanings- for example, 5 represents instability and imbalance, 9 represents absolute completion (seeing as it's a complete number. 3*3=9) There's 3 numbers for people (though places and objects tend to only use the first) that represent character (The actual personality), heart (inner life, fears, hopes, and secrets), and social (the perceived personality). 
The numbers are determined by adding the "value" of the letters in someone's name, adding them up, then reducing the value until you end up with a number that is 9 or under (say you have a value of 49, 4+9=13, 1+3=4). The number that you end up with is the personality number. The same process is repeated with vowels (heart) and consonants (social).

These numbers can be used to see which decisions are favorable. Someone with a personality of 8 will want to schedule events for days whose number is reduced to 8 (8th, 17th, etc.), or buy products that have names that reduce to 8.

That's the basics, one can go deeper to dig out the hidden relationships between the numbers of people and events.