As I happened to be debugging one of my MEDM user screens I noticed that there was some odd behaviour with the
FSS.  It wasn't going out of lock or oscillating but the PZT voltage exhibited some small discrete jumps.  Then
I noticed that it was perhaps due to the ISS acquiring and breaking lock.

    Attached is a plot of the last hour's data.  There's a gap in the data stream starting from about 06:40
and lasting about 13 minutes.  The AOM drive should hover somewhere between 0.500 and 0.550.  This is a better
indicator of how things are (at the moment) rather than the % diffracted power, as this is close to where the
response is linear.  Lower than this value and the response is somewhat parabolic.