Dating 40 Slagelse
The postage is correct: Surface printed matter 5 re, registration 25 re, and catapult mail fee 75 re. Registered cover with "Kbenhavn Lufthavn" airport registry label (not often seen) and airplane pictorial postmarks of same, to AARHUS. C10 is seldom seen on cover, even this late a usage.
Blue Danish LUFTPOST label from the upper right corner of the pane, which thus bears the print date inscription. C7 (VF, but gum soak stain) solo usage on 6 September 1938 cover from TLLSE to MNTT, FINLAND with receiver. Also with red pictorial "flying trunk" handstamp (nice H.
C2 4-BLOCK, #113 x3 [15 re 1926 Airmail; 30 re 1925 Blue Christian X] (block F-VF/Fine, lower left stamp with sealed tear; other stamps F-VF) on 13 September 1926 large piece of cover from "KBENHAVN / LUFTPOST 1". C6 pair, C7, #263 4-block (VF) on 6 September 1938 LARGE-SIZE (180 x 135 mm) cacheted (airplane) Stamp Day cover for first flight SLAGELSE - KBENHAVN, with special Slagelse postmark, violet pictorial (map, plane) handstamp, and Kbenhavn Luftpost receiver. The airmail label (over the edge) is the one position in the sheet showing the form number and print date. "KBENHAVN LUFTHAVN" 28 Jan to poste restante (general delivery) AARHUS 29 Jan and back to "KBENHAVN LUFTHAVN" 29 Jan.
Block of the airmail stamps are very scarce on cover, even on piece. Interesting and somewhat scarce red brown stamp show labels on reverse (ball coach and train/plane). This is the only example of this larger-size cacheted cover that I can recall seeing. Interesting message: It would seem that the card was sent via Sweden to avoid German interference since the war in Europe had already recently started. This specific date/route was not listed by Luning, though many others are.
While not a rarity, this is scarce; I believe that this is the only imperforate example I have had on cover in 41 years.
Lning states that while 4500 perforated stamps were issued, only 500 imperforate were issued -- very scarce in any condition; extremely scarce on cover.