Experimentalists should detect one curious feature in FIg.\ref{525200} above: the error bars  for the measurements above appear to be negligible for the extrema!  This is because the uncertainty shown in this particular graph above does not include all contributions to the uncertainty of the measurement. Rather, it only includes the theoretical uncertainty expected from the uncertainty in polarization angle and not the additional variation in measured voltage  introduced by the measurement apparatus  nor the instability in the diode laser output intensity (primarily due to mode hopping and temperature variations).  These also need to be taken into account! 

Curve fitting

mathematical modeling

 Curve fitting requires a mathematical model, initial estimates for the adjustable parameters in the model, and estimates of the uncertainty in the values of each data point.  Here, we construct a mathematical model based on "Malus's Law" to describe light passing through two linear polarizers, as measured by a powered photodiode: