  This paper describes simple modifications to a demonstration Stirling engine
that allows one to make quantitative measurements of the Stirling cycle. First,
we describe measurements of the $P$-$V$ diagram using an inexpensive pressure
sensor and a common photogate. Then, as a supplement, the engine was run as a
refrigerator by using a rotary tool to turn the flywheel of the engine. A
small, but measurable, temperature difference developed across the body of the
engine.
