Hi the source007, Just a thought... you could create an array to hold the outputs of the first procedure and that would then be the input for the second procedure. Consider this pseudo-code: ;Create some data to store in a file: data=findgen(2,100) ;Open a new file for writing as IDL file unit number 1: openw, 1, 'newfile' ;Write the data from 'data' to the file: writeu, 1, data ;print the first 10 lines to check print, data[*,0:10] ;Close file unit 1: close, 1 Hope this provides some ideas.

IDL passes values by reference so the values will automatically be updated if the variables exist outside of the procedure. Create another procedure to call hr2altaz and altaz2hr such as the one below. pro runner numDataPoints = ;read in hour and dec values, something like: HA = readFromFile() DEC = readFromFile() ;you'll have to implement readFromFile yourself, ; but thats another topic ;if you need to create new or empty arrays to hold all the ; values try this ALT= make_array(numDataPoints); AZ = make_array(numDataPoints); ;also if you want to hardcode the values you can do: ; HA=[1,2,3,4] for i = 0, numDataPoints-1 do begin hr2altaz, HA[i], DEC[i], ALT[i], AZ[i] ;values are passed out by reference altaz2hr, HA[i], DEC[i], ALT[i], AZ[i] ;values are passed out by reference endfor end I hope this helps.