We had some clear skies and I picked a target of opportunity. It was V523 Cas, a classic example of a W UMa contact binary. It was eclipsing around midnight at our local zenith, so I got some clean data (minus a gap during meridian flip). Turns out, V523 Cas is more interesting then just another W UMa binary. (see https://doi.org/10.1111/j.1365-2966.2004.07200.x) It's Max and Min magnitude and period changes over time. I compared my data with data from AAVSO and the variations are plane to see.

Using the published period as a measure, there is a 1209 period span between the two light curves displayed. When I offset the JD of the AAVSO curve to compare them, there was an remaining offset of .199 days, or about 14.22 seconds per period, which corresponds nicely to the observed difference in period.