Hello, I have a sample masked array data as shown below. 1-) When I list the whole array I see the fill value correctly. However below that line, when I do access the 5th element, fill_value flies upto 1e+20. What might be wrong here? I[5]: c.data['Air_Temp'] O[5]: masked_array(data = [13.1509 13.1309 13.1278 13.1542 -- 13.1539 13.1387 -- -- -- 13.1107 13.1351 13.2073 13.2562 13.3533 13.3889 13.4067 13.2938 13.1962 13.1248 13.0411 12.9534 12.8354 12.7392 12.6725], mask = [False False False False True False False True True True False False False False False False False False False False False False False False False], fill_value = 999999.9999) I[6]: c.data['Air_Temp'][4] O[6]: masked_array(data = --, mask = True, fill_value = 1e+20) 2-) What is wrong with the arccos calculation? Should not that result the same as with cos(d) result? I[9]: d = c.data['Air_Temp'][4] I[11]: cos(d) O[11]: masked_array(data = --, mask = True, fill_value = 1e+20) I[12]: arccos(d) O[12]: masked_array(data = 1.57079632679, mask = False, fill_value = 1e+20) Any ideas? -- Gökhan