How do file permissions bits correspond to the values provided to chmod?

The permissions bits applied to a file system object correspond directly to the values which can be specified in the 4 digit tuple supplied to the chmod utility in the following command:

chmod abcd <file system object>

Each value in the digit set abcd is made up of a sum of the values 1 2 and 4. By adding these values together for each digit, a value can be...