In [pulsemodel.py](https://github.com/cpkm/laserdynamics/blob/6ead6f43c2be1161296ed211e6b9d276fc7d614f/pulsemodelling/pulsemodel.py#L627) 4th order dispersion calculated by gratingPair() may be incorrect. It is inconsistent with that calculated symbolically [here](https://github.com/cpkm/beamtools/blob/085c948cf83abcf001af4ed6d0babf10b71dad44/beamtools/diffraction_grating_pair.py#L110).
In pulsemodel.py 4th order dispersion calculated by gratingPair() may be incorrect. It is inconsistent with that calculated symbolically here.