Real numbers are numbers containing decimal points. To be valid, they must have at least one digit on either side of the decimal point:

Quantum deals with real numbers of any size with accuracy up to six significant figures. Numbers with more than six significant figures have the sixth figure rounded up or down depending on the value of the remaining figures.

By default, Quantum calculates cell values in single precision. However, when working with very large numbers, you can produce more accurate results by using the double precision option (dp) on the a statement.

For more information about double precision, see Hierarchy of the tabulation section.