Dear experts, I am encountering a strange behaviour of python data array as below. I have been trying to use the data from a netcdf file(attached herewith) to do certain calculation using below code. If I take absolute value of the same array and look for values <.5 I get a different value than the original array. But the fact is that this particular case do not have any negative values in the array( but there are other files where it can have negative values so the condition is put). I do not see any reason for getting different numbers for values <.5 in case of bt and expected it to be same as that of r2010. If any one has a guess on what is behind this behaviour please help. In [14]: from netCDF4 import Dataset as nc In [15]: nf=nc('r2010.nc') In [16]: r2010=nf.variables['R2010'][:] In [17]: bt=abs(r2010) In [18]: bt[bt<=.5].shape Out[18]: (2872,) In [19]: r2010[r2010<.5].shape Out[19]: (36738,) bt.min() Out[20]: 0.0027588337040836768 In [21]: bt.max() Out[21]: 3.5078965479057089 In [22]: r2010.max() Out[22]: 3.5078965479057089 In [23]: r2010.min() Out[23]: 0.0027588337040836768 *************************************************************** Sudheer Joseph Indian National Centre for Ocean Information Services Ministry of Earth Sciences, Govt. of India POST BOX NO: 21, IDA Jeedeemetla P.O. Via Pragathi Nagar,Kukatpally, Hyderabad; Pin:5000 55 Tel:+91-40-23886047(O),Fax:+91-40-23895011(O), Tel:+91-40-23044600(R),Tel:+91-40-9440832534(Mobile) E-mail:sjo.India@gmail.com;sudheer.joseph@yahoo.com Web- http://oppamthadathil.tripod.com ***************************************************************