Hi, I wrote a IDL program to calculate the yearly average precipitation. It can correctly average 285 images but not more than that. It will give an error saying that result is invalid and I tried the equation by using the ENVI band math. It also give an error. So please help me to solve this problem it is strange even though.. pro Average_images_batchP compile_opt idl2 ENVI, /RESTORE_ALL ; envi_batch_init, log_file='batch.txt' ; input_dir =DIALOG_PICKFILE(/DIRECTORY, TITLE='Select folder') stack_file = FILE_SEARCH(input_dir+'*.dat',COUNT=count) fid = lonarr(count) pos = lonarr(count) dims = lonarr(5,count) for i=0L,count-1 do begin st_file = stack_file[i] envi_open_file,st_file, r_fid=t_fid if (t_fid eq -1) then begin envi_batch_exit return endif fid[i] = t_fid pos[i] = 0 envi_file_query, t_fid, $ ns=r_ns, nl=r_nl, nb=r_nb ,sname=rname dims[0,i] = [-1,0,r_ns-1,0,r_nl-1] print,r_ns,r_nl if(i eq 0)then begin expstring='(b'+string(i+1) endif else begin expstring=expstring+'+b'+string(i+1) endelse endfor expstring=STRCOMPRESS(expstring+')/'+string( float(count)),/REMOVE_ALL) print,expstring cd,'E:\Academic\Research\Processing\percipitationSubset32\' out_name=STRCOMPRESS('percipYearlyAvg'+'.img',/REMOVE_ALL) ;out_name=STRCOMPRESS('watershed_'+string(h)+'.dat',/REMOVE_ALL) envi_doit, 'math_doit', $ fid=fid, pos=pos, dims=dims, $ exp=expstring, out_name=out_name, $ r_fid=r_fid ;endfor envi_batch_exit end