This page-by-page annotation is organized by sections, as delineated by the seven squares (sprockets) which separate each section. The page numbers for this page-by-page annotation are for the original Viking edition (760 pages). Editions by other publishers vary in pagination the newer Penguin editions are 776 pages; the Bantam edition is 886 pages.
Contributors: Please use a 760-page edition (either the original Viking edition with the orange cover or the Penguin USA edition with the blue cover and rocket diagram there are plenty on Ebay for around $10) or search the Google edition for the correct page number. Readers: To calculate the Bantam edition use this formula: Bantam page # x 1.165. Before p.50 it's about a page earlier; as you get later in the book, add a page.
Finally, profound thanks to Prof. Don Larsson for providing the foundation for this page-by-page annotation.
Entre Ríos is a province of Argentina, located in the Mesopotamia region, in the northeast of the country. It borders the provinces of Buenos Aires (south), Corrientes (north) and Santa Fe (west), and Uruguay in the east.
a brick labyrinth that had been a harmonica factory
Jorge Louis Borges, who has been mentioned in this section, has one book entitled Labyrinths, 1962 in English.
A harmonica player is a musician. Musicians are favorite artists in Pynchon's vision.
Harmonicas turn up again in Against the Day.
Weisenburger concludes this must be the Hohner factory in Trossingen. Slothrop's mouth harp is a Hohner, while the company is also a major producer of accordions, the key intrument in Argentinian music. In fact, when tango became the rage all over Europe, accordions were marketed as Tangoharmonika (Mundharmonika is German for mouth harp).
the smell of freshly brewed mate
Yerba mate is the national drink of Argentina. It is also popular in Paraguay, Uruguay and southern Brazil. It reportedly creates a mental state of wakefulness, focus and alertness reminiscent of most stimulants, but lacks the negative effects typically created by other such compounds, such as anxiety, diarrhea, "jitteriness", and heart palpitations. According to the classical Argentine way, the act of drinking yerba mate is a highly stylized, ritualistic process:
- The gourd is filled two-thirds of the way with moistened mate herb. Hot water is then poured into the gourd. The person sucks the mate water out of the gourd with the bombilla, with the strainer holding out the actual mate leaves. When the water is gone, the gourd is refilled by the server with hot water and passed to the next person in the group. When that person finishes, the gourd is handed back to the server for another refill. 
No destinations. No fixed itinerary.
Like Bennie Profane's yo-yoing that starts V.
The pun is obvious enough, but it just might derive from John Frankenheimer’s The Manchurian Candidate (1961). The main character, the humorless Raymond Shaw (Lawrence Harvey), calls attention to the pun as the first joke he’s deliberately made.
Martín Fierro is an epic poem by the Argentine writer José Hernández. The poem was originally published in two parts, El Gaucho Martín Fierro (1872) and La Vuelta de Martín Fierro (1879). The poem is, in part, a protest against the Europeanizing and modernizing tendencies of Argentine president Domingo Faustino Sarmiento. Wikipedia
390:1.2 It took the Dreyfus affair to get the Zionists out and doing
Theodor Herzl, a secular and highly assimilated Austro-Hungarian Jew covered the Dreyfus trial for a Viennese newspaper, and was witness to the anti-Semitic demonstrations in Paris following the judgment. It was this experience which convinced him of the futility of assimilation and combating anti-Semitism is the diaspora, and resulted in the concept of a separate Jewish state. The analogy is followed up with "settlement" in "the Heath".