(Top panel). Onsala spectrum (thick light red line) and FCRAO (thin black line) of ¹²CO in Position 15. The line that shows at +10.5 km s^-1 is telluric in origin and should be ignored here. (Bottom panel). Onsala OFF (about 20′ west from Position 15) spectrum used as a check for the telluric line. The line at -10.5 km s^-1 probably picks up some gas in the surroundings of the cloud. See the text for further details.