Frequency and Velocity scaling of Plots

It is now possible to produce plots which have the image sideband frequency along the top axis. To get this, all you have to do is to choose the absolute frequency options in SET-X-SCALE. Note however that it is unlikely to be correct unless the display frame is the one in which the source is at rest. Since you *may* have observed with (say) the LSR velocity not equal to that of the source itself, I can't protect you from this. But in most cases it will be sufficient to do

>> SET-VELOCITY-FRAME yes lsr radio vlsr

That is, choose a velocity reference frame which is defined as having velocity offset with respect to the standard of rest the same as that of the source itself (modify as appropriate for heliocentric, geocentric or telluric frames, and for different velocities or velocity definitions).

HOWEVER... You must realize that most plotting packages, PGPLOT amongst them, accept REAL*4 numbers only. So if you display things in absolute frequency, it is not possible to get velocities accurate to better than a couple of MHz in three hundred odd GHz, no matter how accurately they are calculated internally in SPECX. For more accurate displays, choose a convenient reference frequency in the absolute frequency option in SET-X. For example, if you have a set of lines in the range 338 - 339 GHz, then choose a reference frequency of 338 GHz, and remember to add this back on to any frequency you determine with FIT-GAUSSIAN, or using the cursor.

My thanks to Remo Tilanus in particular for his help, provision of DAS data, and rapid turn around of queries while we were solving the problems associated with the DAS. My apologies to anyone who may have been inconvenienced by problems in the Beta-test version -- I hope you appreciate that it was the only way to make DAS data available at all.