Jerry W. Lewis wrote...
....
Plot the data as an "XY (Scatter)" chart and add a 6th degree polynomial
trendline (format to scientific notation with 14 decimal places); if
there is an appreciable difference between the graph and formula
coefficients, then the graph coefficients are better.

David Braden has posted code to directly extract coefficients from the
displayed chart trendline equation into cells
....

Meaning that Microsoft is still using different pieces of code for
LINEST and chart trend lines? And the older, trend line code is
better? If so, it begs the question why Microsoft squandered their
money changing the LINEST code rather than just using the trend
line code for LINEST.