The Number1 through Number20 fields are custom fields that store any numeric information you want to include in your project relating to tasks, resources, or assignments. The default number is 0.
There are several categories of Number1-20 fields.
Data Type Number (number field: A type of field whose content is a number. The maximum value allowed in this field is 999,999,999,999.99.)
Number1-20 (task fields)
Number1-20 (resource fields)
Number1-20 (assignment fields)