What is the accuracy of the datenum function?

What is the accuracy of the datenum function? How many decimal places are retained for the seconds portion of time? When evaluating the elapsed time between dates and times, what decimal place in seconds is it accurate to?

Answer 1

[Andreas]

Milliseconds

Answer 2

[Stephen23]

Although not clearly documented, in my experience datenum and friends offer repeatable operations down to milliseconds.

Note that the theoretical limit of the double type is just less than a millisecond:

 >> (3000*365*24*60*60)/pow2(52)
 ans =   2.1007e-005
 >> eps(3000*365)*(24*60*60)
 ans =   2.0117e-005

https://www.mathworks.com/matlabcentral/answers/45765-what-is-the-precision-of-a-matlab-datenum

http://www.mathworks.com/matlabcentral/newsreader/view_thread/250872

Answer 3

[Peter Perkins]

Phil, unless you're using pre-R2014b, you are probably better off using datetime instead of datenum. As others have said, the practical limit of datenums is on the order of .1ms. This is one of the many improvements that datetime offers: precision down to nanoseconds.