Richard, As I promised I have put the two plots in my web side: www.aoc.nrao.edu/~lkogan DELZN32.PS is the renamed existed file 3 tirm polynomial for zenith atmosphere; 2 term polynomial for clock. APARM = 0 3 2 DELZN22.PS 2 term polynomial for zenith atmosphere; 2 term polynomial for clock APARM = 0 2 2 LK