If what you have in mind is the usage of
time shell builtin, then 3 digit precision is the design limitation - as per
The value of this parameter is used as a format string specify‐
ing how the timing information for pipelines prefixed with the
time reserved word should be displayed. The % character intro‐
duces an escape sequence that is expanded to a time value or
other information. The escape sequences and their meanings are
as follows; the braces denote optional portions.
%% A literal %.
%[p][l]R The elapsed time in seconds.
%[p][l]U The number of CPU seconds spent in user mode.
%[p][l]S The number of CPU seconds spent in system mode.
%P The CPU percentage, computed as (%U + %S) / %R.
The optional p is a digit specifying the precision, the number
of fractional digits after a decimal point. A value of 0 causes
no decimal point or fraction to be output. At most three places
after the decimal point may be specified; values of p greater
than 3 are changed to 3. If p is not specified, the value 3 is
For seemingly more precise measurements, you can try using
date with customized output formatting to show nanoseconds:
echo "Elapsed: $( Tend-Tstart |bc -l) nanoseconds"
However, notice that in both cases (
date), you have some overhead, as the system takes some time to run the starting/stopping commands. The overhead is smaller for
time, thanks to it being a builtin. So the three-digit limit is there for a reason: the rest is just random garbage.
See also this similar question, though the accepted answer contains a little bug currently.