function ch4vp, t
; Return vapor pressure, in microbar, as a function of temperature
a=[1.71271658e1, -1.11039009e3, -4.34060967e3, 1.03503576e5, -7.91001903e5]
p = exp( total((t^(-findgen(5))) * a))* 1.33322e3
return, p
end