I've been studying the history of psychology and neuroscience such as the studies conducted by von Helmholtz and Wilhelm Wundt. From what I've read it seems to me their studies depended on technology that could record time on the scale of milliseconds (i.e. measuring reaction times and speed of neural transmission. How exactly did they measure these types of things with precision back in the late 19th century?
Sorry in advance if this is the wrong sub.
By early 19th century there were sophisticated mechanical stop-watches that used a system of multiple redundant "Balance wheel"-style escapements to be able to measure time to within a quarter of a second, and sometimes as small a unit as 1/16th of a second.
These early stopwatches were hand-built marvels with prices to match. Stopwatches accurate to 1/4th of a second seem to have come into wider use for sports records (and sport betting, especially on horse races) sometime in the mid-19th century.
Stopwatches accurate to small fractions of second didn't exist commercially before the introduction of the Heuer "Micrograph" in 1916.
So Helmholtz in doing his famous nerve-impulse experiments in 1852 probably would have had access to a scientific chronometer able to relaiably and accurately measure within a 1/4th of a second, and maybe even smaller than a 1/10th of second, depending on his resources.
To the best of my understanding, genuinely 1/1000th of second precision was functionally impossible before the invention of modern quartz mechanism chronometers in the 1930s.
As an aside, although experimental quartz-resonators chronographs had been built as scientific and laboratory equipment as early as 1927, they remained crazy-expensive and too large and fragile to use in a pocket-watch or wristwatch until the development of modern solid-state transistors in the early 1960s.