The 1 peso map with boundaries, the 1pL, was printed in the first paper and the first watermark. The paper is cream in color. The gum is yellowish. The watermark is grainy and with a medium RA in circle, and all features of the watermark are clear. The watermark shows up sideways in both directions (reading downwards or upwards). Quick links: main publications page / issues studies ( 001: 1pL / a new plate variety / covers batch 1) / flash slide shows (thanks to Picasa/Google!)

As of April 2008, most of the used specimens and covers I am using for this study are in book 1 of the reference collection. Also as of this date, the study uses approximately 200 used specimens, a handful of mint specimens, and approximately 20 covers. This stamp is uncommon, but not rare. This stamp is Kneitschel 501 and Klass 539. There are two plate varieties that are recognized by these catalogs: (Kn 501a, Kl 539a) Line running the length of Argentina region, and Kl 539b Retouched region in left denomination circle.

(Kn 501a, Kl 539a) Line running the length of Argentina region

Kl 539b Retouched region in left denomination circle

Below is an early use of the 1pL, on January 15, 1936, to Bern, Switzerland. The Argentinean postmark is the commonly-used 'Servicio Aeropostal' marking. Also here is a detail of the two 1pL stamps on this cover.

Below is a mid-January use to Prague, Chekoslovakia. This cover is postmarked 'Servicio Aeropostal' on January 18, 1936. The time of travel for this cover is five days.

The earliest cover I am able to find is from January 4, 1936

After I began this study, I was also able to find (Kn 501a, Kl 539a) Line running the length of Argentina region on cover dated June 7, 1936