Apparently I got it backwards...? So THIS is a '51' Vac?... http://www.ebay.com/itm/Vintage-Parker-51-Vacumatic-Pen-Maroon-w-Silver-Two-Tone-Top-/201446893941?hash=item2ee72ba975 and THIS is a '51' Aerometric?... http://www.ebay.com/itm/Vintage-Parker-51-Aerometric-Fountain-Pen-Pencil-Set-1940s-Canada-/171967097205?hash=item280a09a975 I stand corrected...? Now that there is the World Wide Super Highway, you think that it would be easier to discern these things... LOL-apologies in advance, long day of teaching........