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.
20.21 What it is is a graphite cylinder
The contents wiull be revealed on pp. 71-72.
Does anyone know how TRP pronounces this? Is it just a stutter? (It will recur in all his subsequent books.)
Not "tour of duty," as in Weisenburger, but "temporary duty."
20.37 East End This is the East End of London, particularly heavily bombed by the Germans in the war as London's docks were situated there. It was, and still is, the area where the poorest people of London live. Famously, Queen Elizabeth's mother made a royal visit there during the war where she was enthusiastically received.
21.07 A lot of stuff prior to 1944 is getting blurry now.
Even this early in the novel, Slothrop has problems with his "temporal bandwidth." His memories of the Blitz (21.08) put him in London no later than May 1941, and possibly as early as September 1940.
21.32 these three years
This puts Slothrop and Tantivy together (presumably at ACHTUNG) since Dec. 1941.
21.35 Tantivy's guest at the Junior Athenaeum
According to the London Encyclopedia the Junior Athenaeum purchased Hope House at 116 Piccadilly in 1868, owning it until the building was demolished in 1936. The JA appears to have closed its doors in 1931, making this a possible anachronism. The Athenaeum Club proper is the most intellectually elite of the gentlemen's clubs; Darwin, Dickens and Trollope were members and Michael Faraday was secretary of the first committee.
While sources do agree with Weisenburger that the term "86" might originate in rhyming slang (for "nix"), they also agree that it was first used in the restaurant business to indicate menu items that were no longer available. The wider usage here may not have originated until the 1950s.
22 a build out of the chorus line at the Windmill; also p39 "It's not backstage at the Windmill"
The Windmill opened in 1932 in a building which had been the Palais de Luxe Cinema and then a theatre. It featured comedy and burlesque revues. The only London theatre to remain open throughout the war, the Windmill continued until 1964 when it became a cinema, reverted to a strip club in 1973, became a theatre/restaurant in 1982 and finally re-opened as a strip club in 1986. From a recent advertisement: "The Windmill International - London's Premier Tableside Dancing Club with 75 Beautiful Dancing Girls who will perform tableside for you - full Nudity - fantastic stage and light show - Dress Smart".
22.04 Frick Frack Club
The term "frick and frack" is often used to designate two people or almost any two items closely associated with each other. The term originates from the stage names of a pair of Swiss skaters who starred in ice shows in the 1930s. Pynchon probably chose the name more for its senseless alliteration (like "Kit-Kat Club") than any specific meaning.
Thomas Hooker... wilde Thyme
Thomas Hooker (July 5, 1586 – July 7, 1647) was a prominent Puritan religious and colonial leader, who founded the Colony of Connecticut after dissenting with Puritan leaders in Massachusetts. He was known as an outstanding speaker and a leader of universal Christian suffrage. 
"wilde Thyme" also brings to mind "Wild Tyme", song by Jefferson Airplane on their 1967 LP After Bathing At Baxter's 
A beef extract--its main use is as a flavouring for soups, and as a drink when you put a teaspoon of the stuff in a mug of boiling water. The method for making the extract was perfected by Justus von Liebig, who co-founded the eponymous London based company.
Women's Royal Naval Service - British civilian support group of war effort
23.25 Ike jacket
Humber is a British automobile marque which could date its beginnings to Thomas Humber's bicycle company founded in 1868. Following their involvement in Humber through Hillman in 1928 the Rootes brothers acquired a controlling interest and joined the Humber board in 1932 making Humber part of their Rootes Group. The range focused on luxury models, such as the Humber Super Snipe. 
The Morrison shelter, officially termed Table (Morrison) Indoor Shelter, had a cage-like construction beneath it. It was designed by John Baker and named after Herbert Morrison, the Minister of Home Security at the time. It was the result of the realisation that due to the lack of house cellars it was necessary to develop an effective type of indoor shelter. The shelters came in assembly kits, to be bolted together inside the home. They were approximately 6 ft 6 in (2 m) long, 4 ft (1.2 m) wide and 2 ft 6 in (0.75 m) high, had a solid 1/8 in (3 mm) steel plate “table” top, welded wire mesh sides, and a metal lath “mattress”- type floor. Altogether it had 359 parts and had 3 tools supplied with the pack. 
25.06-07 Slothrop’s Progress . . . a parable
"Slothrop’s Progress" echoes John Bunyan’s Puritan allegory The Pilgrim’s Progress. The word "parable," interestingly, comes from the same root as "parabola."
Slothrop's Progress may be Time itself. Sir Arthur Eddington coined the term "time's arrow" to describe entropy's progress and time's irreversibility-- i.e. "as the universe gets older, it becomes more disordered, following the second law of thermodynamics." Entropy's progress defines time. Cf. Scientific American, Jan 2008, p.26 for more.
25. 29 Bond Street Underground station This is a station in the wealthier West End of London - also a site on the British version of 'Monopoly'
26.30 back home in Mingeborough, Massachusetts
The Berkshire town was first created by Pynchon in the short story "The Secret Integration," set in the mid-1960s. This story also introduced the Slothrop family, in the person of Hogan Slothrop, who is apparently the son of Tyrone’s brother. Minges (or "midges") are small, biting insects. However, "minge" was originally also a British slang term for a woman's pubic hair, now generalised to the female genitals.
26.33 British Double Summer Time
Correspondent Igor Zabel explains this term: " . . . in Britain they had, during the war, the clocks an hour ahead in the winter time and two hours in the summer time."
26.37-38 Death is a debt to nature due . . . so must you.
Weisenburger claims that this epitaph, with its debt to "nature" rather than God, would be heretical to Puritans. That might be so, but the inscription was fairly common on tombstones in the northeast from the mid-1700s until the early 1800s, a range that includes Constant’s 1760 death.
27.04 Variable Slothrop
The son of "Constant": The two names play a mathematical pun and suggest the family’s decline as well. Both names seem to be a pun as well on the name of Puritan minister and Harvard president, the Rev. Increase Mather of Massachusetts Bay Colony and his son, Cotton Mather. Increase attempted to decrease the heat surrounding the Salem Witch Trials through a series of sermons seeking moderation in the use of spectral evidence, even though he defended the trials and the judges. Parallels: Second law of thermodynamics - heated trials cooling. Increase-Cotton-Constant-Variable --
27.31-33 They began as fur traders, cordwainers, salters and smokers of bacon, went on into glassmaking, became selectmen, builders of tanneries, quarriers of marble.
28.02 converted acres at a clip into paper
A paper clip? A likely reference to Operation Paper Clip, the OSS program to recruit Nazi scientists to work for the US and deny them to the Russians. Von Braun was brought to the US under this program.
28.02-03 paper—toilet paper, banknote stock, newsprint
The Berkshire Hills describes several paper mills in the region and notes the importance of the industry. One producer, Crane and Company, first used the term "bond" for high-quality paper and provided special paper for U.S. currency from 1879 on . Another company, in the town of Lee, gave the "first practical demonstration in America of the process of manufacturing paper from wood pulp instead of rags" .
The Somerset Club is a private social club in Boston, Massachusetts, founded perhaps as early as 1826. The original club was informal, without a clubhouse. By the 1830s this had evolved into a group called the Temple. In 1851 the group purchased the home of Benjamin W. Crowninshield, located at the corner of Beacon and Somerset Streets. Originally called the Beacon Club, it was renamed the Somerset Club in 1852. In 1871 the Somerset Club purchased the David Sears townhouse at 42 Beacon Street on Beacon Hill. Originally designed by Alexander Parris and built in 1819, Sears had added to the house in 1832 and had built the adjacent Crowninshield-Amory house at 43 Beacon Street for his daughter. The land on which the house stood was originally part of an 18-acre (73,000 m2) parcel owned by John Singleton Copley, who called it "his farm on Beacon Street." Eventually the Club bought 43 Beacon Street and joined the two houses into one large clubhouse. 
V28.33-34 Harrimans and Whitneys gone
The Harrimans are mentioned in passing several times in The Berkshire Hills as being among the wealthy families who spent their summers in the region. William C. Whitney, President Cleveland’s Secretary of the Navy, is specifically mentioned as the founder of a vacation colony in Lenox in 1886 .
Tyrone Slothrop’s brother, presumably the father of the Hogan Slothrop of "The Secret Integration," set in the Berkshires a generation later.
Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. 
- The Berkshire Hills', Funk & Wagnalls Company, New York, 1939
- Ibid, p. 238
- Ibid, p. 143
- Ibid, p. 224
Beyond the Zero
Un Perm' au Casino Herman Goering
In the Zone
279-295, 295-314, 314-329, 329-336, 336-359, 359-371, 371-383, 383-390, 390-392, 392-397, 397-433, 433-447, 448-456, 457-468, 468-472, 473-482, 482-488, 488-491, 492-505, 505-518, 518-525, 525-532, 532-536, 537-548, 549-557, 557-563, 563-566, 567-577, 577-580, 580-591, 591-610, 610-616