MDAC 2.5 SDK - OLE DB Programmer's Reference
Appendix A: Data Types

Precision of Numeric Data Types

The following OLE DB data types are used to represent numeric values. Each type has a corresponding maximum precision value that indicates the maximum number of base 10 digits that it can store. The radix of the precision for all numeric types is 10. The maximum precision returned by the provider in the COLUMN_SIZE column of the PROVIDER_TYPES schema rowset is the maximum possible precision for the data type that is supported by the data store. For example, if a data store can support a maximum precision of only 28 for a DBTYPE_NUMERIC column, the provider returns 28, not 39, as the maximum precision.