Introduction This section contains functions that make many date computations easier to perform. Date-type values have been a feature of the xBASE language standard, and is preserved in Clipper. In spite of this, it is always necessary to develop UDFs to execute certain technical financial computations. Clipper Tools offers an alternative that not only spares you the work of writing a UDF, but also provides implementation in Assembler to guarantee fast execution. This chapter also contains clock time functions. These include time changes, time span computations, time control of loops, and memory- resident clock display. Please note that valid date tests are already carried out in Clipper. Clipper internal date tests cannot be canceled, so it is impossible to implement an individual UDF for error handling , if there is an invalid date. Clipper always replaces an invalid date with a null date. These internal tests are carried out by keyboard input, as well as by CTOD() allocation. For this reason, there are no examples with invalid dates in the date function descriptions. Rather, the result of a function with a null date is shown.