problems with the surge calculations

[gpagliuca]

fa.gists.surge_calc(data.index, data['21mm'], drain)

AttributeError Traceback (most recent call last) in () ----> 1 fa.gists.surge_calc(data.index, data['21mm'], drain)

C:\Apps\anaconda\lib\site-packages\pyfas\gists.py in surge_calc(time_series, liq_flowrate, drain) 6 def surge_calc(time_series, liq_flowrate, drain): 7 dt = np.diff(time_series) ----> 8 dt.units = pq.h 9 surge = (np.convolve(liq_flowrate, 1)[1:]*liq_flowrate.units-drain)*dt 10 surge.base[surge < 0] = 0

AttributeError: 'numpy.ndarray' object has no attribute 'units'