why does timeit go usec then nsec code example

Example 1: how to time python code

from timer import Timer
t = Timer()
t.start()
# Run stuff here.
t.stop()

Example 2: how to use timeit in python 3

import timeit
import_module = "import random"
testcode = ''' 
def test(): 
    return random.randint(10, 100)
'''
print(timeit.repeat(stmt=testcode, setup=import_module))