Just tried when the code starts to malfunction:

    In [17]: check(1./200000000)

    In [18]: check(1./2000000000)
    ---------------------------------------------------------------------------
    AssertionError                            Traceback (most recent call last)
    <ipython-input-18-900ddfd8f3c9> in <module>()
    ----> 1 check(1./2000000000)

    <ipython-input-10-d41f18e09b24> in <lambda>(x)
    ----> 1 check = lambda x: assert_almost_equal((1. / x) % 1, 0, decimal=10)

    /Users/hannes/.virtualenvs/skimage/lib/python2.7/site-packages/numpy/testing/utils.pyc in assert_almost_equal(actual, desired, decimal, err_msg, verbose)
        466         pass
        467     if round(abs(desired - actual),decimal) != 0 :
    --> 468         raise AssertionError(msg)
        469 
        470 

    AssertionError: 
    Arrays are not almost equal to 10 decimals
     ACTUAL: 0.9999997615814209
     DESIRED: 0

But I don't think a scale factor of 2 billion is reasonable... ;-)