[racket] How can I measure time in nanoseconds?

The closest approximation I can find in the documentation is 
current-milliseconds? I require more accuracy in my project, 
specifically, nanosecond accuracy. I do apologise if I've missed this 
information in the documentation, if so can anyone point me to the right 
place? Or recommend a method to obtain more accuracy?

Thank you for your time,

Horace.


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