AOD_hist = AOD_hist+HISTOGRAM(AOD_screened, BINSIZE=0.01) when I use the histogram function, the first bin is wrong. It gives first bin value as 54 where as if I print, with the following commands I get 63.0 Why is the difference? IDL> a=TOTAL(AOD_screened LT 0.01 OR AOD_screened EQ 0.01) IDL> print, a 63.0000 IDL>