The Hartstone benchmark is a set of timing requirements for testing a system's ability to handle hard real-time applications. It is specified as a set of processes with well-defined workloads and timing constraints. The name Hartstone derives from HArd Real Time and the fact that the workloads are presently based on the well-known Whetstone benchmark. This report describes the structure and behavior of an implementation in the Ada programming language of one category of Hartstone requirements, the Periodic Harmonic (PH) Test Series. The Ada implementation of the PH series is aimed primarily at real-time embedded processors where the only executing code is the benchmark and the Ada runtime system. Guidelines for performing various Hartstone experiments and interpreting the results are provided. Also included are the source code listings of the benchmark, information on how to obtain the source code in machine-readable form, and some sample results for Version 1.0 of the Systems Designers XD Ada VAX/VMS - MC68020 cross-compiler.