FYI, automation of coefficient calcs has been added. No more need for spreadsheets. To achieve this, an AFC analyzer function needed to change how autofocus<date>.txt files are created/stored. It also needed to change the CSV file format to include a filter offset. This implies that old autofocus<date>.txt files, while still very valuable, need to be pre-processed before AFC can analyze them. Old files will need to be concatenated into a single file with filter offset values added. If anyone out there is good with awk/sed scripts (and might be willing to help write a simple concat/conversion script), let me know. It probably took me longer to type this than a good script developer would take to write a script to convert the old files! FWIW, AFC could just start over collecting data for analysis, but it would be a shame to ignore anyone's precious historical data. The old & new autofocus CSV file formats are below:

Old format (one file per date; "autofocus<date>.txt"):
date, time, position, temperature, filter, HFR, altitude
2021-02-19, 7:24:37, 54295, 15.1, Luminance, 1.382, 52.0
2021-02-19, 8:32:02, 53949, 14.4, Red, 1.791, 74.2
etc., etc., ....

New format (all dates in one "autofocus.txt" file, plus added filter offset for each row):
date, time, position, temperature, filter, offset, HFR, altitude
2021-02-19, 7:24:37, 54295, 15.1, Luminance, 0, 1.382, 52.0
2021-02-19, 8:32:02, 53949, 14.4, Red, 100, 1.791, 74.2
etc., etc., ....

Be aware that unless a script/tool is provided to convert old files, if you want to analyze your historical data, you'll have to convert these (or just let AFC start over collecting data to be analyzed for coefficients calculation).

Also FYI: A modification to the focus GUI (new tab) is in the works. It replaces the "gen-1" AFC configuration file. Consistent with the config file, separate controls for enabling/disabling autofocus start position ( the AF "seed"), updating focus between Light frames, <optional> altitude residuals compensation, and performing historical analysis (calculating coefficients) are anticipated. A focuser move control will suppress sending move commands until a threshold value is crossed. Finally, a couple of buttons will allow updating analysis (coefficients update) and saving settings.

Finally, a git branch was created for the first code revision (updated last night for the latest kstars/ekos release). While usable now by those with development environments (via config file control), this branch hopefully will be updated with a GUI in the coming days/weeks. A hearty thanks to the volunteer alpha testers who provided early support as AFC progressed! Hopefully in the near future, all who have reasonably stable motorized focusers and an ambient temperature sensor will enjoy more sophisticated focus control(s). I hope to have good weather for several nights remote testing on-sky this coming week and will report findings afterward. Until then, Cheers, Doug