The Buenos Aires 1859 1p "In Ps" tête-bêche pair, also known as the “In Peso” tête-bêche Pair, is the only known specimen of an inverted error on Barquitos postage stamp issued by the sovereign state of Buenos Aires.

Owing to time constraints, the Mint decided to modify the 4 and 5-peso plates to create the 1 peso and 4 reales (half-peso) stamps, respectively.

The nails show up as white holes in the design, having been recessed below the level of each metal cliché.

[5] Even Barquitos stamps without notable errors are considered a great classic and highly prized.

[3] This pair were exhibited in 1986 as part of the Aristocrats of Philately displays at Ameripex and again at Anphilex in 1996.

They were previously owned by Alfred H. Caspary until 1958, Lars Amundsen, Joseph Schatzkés, John Robert Boker, Jr., and Gabriel Sanchez.