  RX J0806+15 shows a prominent intensity variation on a period of 321.5 sec.
This has widely been interpreted as the binary orbital period, although this
remains controversial. We have been monitoring the precise period of RX
J0806+15 for a number of years. By measuring the rate of change we can help
distinguish between competing physical models. New observations obtained
between Nov 2003 and Feb 2004 show that the period decrease already reported by
Hakala et al (2003) and Strohmayer (2003) is continuing. We discuss how
reliably we can determine the period of RX J0806+15 using our technique and
evaluate the current models which have been proposed to account for the
observational properties of this source.
