Building an executable with pyinstaller is a fraught affair on Windows

From trial and error I've found that the most reliable way to build is to:
1) Install python.org Python.
2) Do not use a virtualenv (some hooks don't work) to build the executable
3) Don't use conda, numpy/scipy/matplotlib/pyqt automatically want to install
   mkl, which isn't GPL compatible
4) Install with pip all the requirements into the python.org distribution
   (periodictable, numpy, scipy, cython, pyinstaller, matplotlib, pyqt6, qtpy
    corner, ptemcee)
5) pip install refnx
6) pyinstall.