Originally Posted by W.D.Clinger
Parentheses added by me for clarity of context.
A slight reminder on this point...
NIST only derived their displacement formula to velocity.
The only acceleration model
used is the linear regression
, and it is from that linear regression that their stated metrics are generated...
NIST used the datapoints circled in red
(which were themselves determined by central difference approximation
from the underlying displacement data) to calculate their stated linear regression (the red
v(t) = -44.773 + 32.196t
It is this linear regression which is used to specify the rough 2.25s *freefall* period.
That fact is made even clearer if we actually look at the implied NIST acceleration function (which they did not use) and check the period of time which it can reasonably be said to approximate gravitational acceleration...
I have taken the liberty of marking a 2.25s duration in red
and gravitational acceleration in cyan