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George wrote:
Typical reaction times are on the order of .25 s; the stopwatches we use
display precision on the order of +/- 5 ms. I suggest to my students
that claiming the instrumental limit as the uncertainty of their
measurement is unreasonable, especially for a single trial. Repeated
trials characteristically show a standard deviation consistent with
reaction time, rather than the stopwatch's displayed precision. (1)
That's not at all what I find. In my experience, good technique with
a stopwatch of sufficient instrumental precision easily results in
measurement uncertainties (derived properly from repeated
measurements) that are far smaller than typical reaction times. (2)
For instance, I can readily obtain a series of measurements for a
ball rolling down an inclined plane that has a standard
deviation less than 50 ms.
Moreover, even if the two were more consistent, I would argue
strongly that the uncertainty in such timing measurements--where
nothing is taking anyone by surprise--has essentially nothing to do
with the phenomenon that is properly called "reaction time." (3)
John Mallinckrodt
Cal Poly Pomona