Below is a detail from a used block of six of the 10c Rivadavia red.

Below is a philatelic envelope posted with all of the low values that were issued in the 1E paper.

Below is a 5c1E with the RA reading from bottom to top.

The most common type for the small format values is for the RA to read from top to bottom, and for RA to be readable from the back, or inverted when the stamp is viewed from the front-I show an example below left. I find approximately 10 percent of the 10c Rivadavia red stamps I examined (a few hundred) to have the watermark reading from bottom to top, as shown below right.

Here are scans for two large blocks of the 1c1E. Because this stamp has a light color, it is ideal for a back scan of the watermark.