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\section{Timing data}  The data has been taken from \cite{Potter_2011}. All timing stamps are in BJD using the TDB time scale. No further transformations needed. A total of 42 timing measurements exist. However, Potter et al. have discarded data points. See their text for details. In this analysis I will consider the full set of timings as a start. Later the analysis chain can be repeated with any discarded timing measurements.  \section{Linear ephemeris - fitting a straight line} line using LINFIT}  In general I am using IDL for the timing analysis. The cycle or ephemeris numbers have been obtained from IDL> ROUND((BJDMIN-TZERO)/PERIOD) where BJDMIN are all 42 timing measurements, TZERO is an arbitrary timing measurement that defines the CYCLE=$E$=0 and PERIOD is the binary orbital period (0.087865425 days) and was taken from \cite{Potter_2011}, Table 2. As a first step I used IDL's LINFIT code to fit a straight line with the MEASURE\_ERROR keyword set to an array holding the timing measurements errors (Table 2, 3rd column, Potter et al. 2011). This way the square of deviations are weighted with $1/\sigma^2$ where $\sigma$ is the standard timing error for each timing measurement. The resulting reduced $\chi^2$ value was 95.22 with the ephemeris (or computed timings) given as  \begin{equation}  T(E) = BJD~2450021.77890(6) + E \times 0.0878654291(1)   \end{equation}  \section{Linear ephemeris - fitting a straight line using CURVEFIT}