Method first. A model number has at most three working parts: a prefix (the letters), a payload (the digits that mean something), and ceremony (the digits that don’t). The craft is knowing which is which before the dealer does. Four classes cover the industry; memorise them and burn this page — or laminate it, which in this household amounted to the same devotion.

Class I — the honest declarers

These brands print the speed on the nameplate and dare you to check. Toshiba’s BD line is the clean intercept: first two digits are the copies per minute — 2060, 3560, 4550, 9050 — verified almost exactly against a period EPA catalogue. (“BD” itself — “Beauty Duplicator,” says dealer folklore — remains unverified lore.) Ricoh’s FT series transmits from the other end: last two digits are the cpm, verified for the FT4527 and FT5535 in the service manual, inferred across the rest.

Minolta’s Di digitals barely bother encrypting: the number is the ppm — Di620, 62 a minute, confirmed at the flagship, the rest following the pattern. Panasonic’s FP speaks honesty in two dialects: leading digits in the xx80 family (FP-1780, 17; FP-4080, 40), tail digits in the Medallion 77xx (7735, 7742, 7750 — 35, 42, 50). Same truth, different word order.

Class II — the dynasty-namers

Here the prefix is the message and the digits are house business. Canon runs three dynasties: NP (“New Process,” patented 1965 — the letters commemorate the physics), CLC for the colour court, PC for the cartridge commoners. Trust the prefix, audit the digits: the NP-6030 does 30 cpm and the NP-6050 does 50, but the NP-9800 does 83. Mita’s DC dynasty runs from the DC-15 of 1979 to the DC-9285 — and the department files a minority report: no doctrine is declared in the record, yet the EPA dataset shows the 90s fleet’s leading digits tracking speed almost perfectly (1820 at 18, 9285 at 92). A speed-declarer on dynasty papers. Kodak’s Ektaprint numbers are pure heraldry: the 95 runs 60 cpm, the 235 about 85. Seniority, not speed.

Class III — the era-coders

Sharp is read the way a geologist reads a cliff: the prefix is a stratum. Z is the personal-cartridge bed; SF — the Sharpfax lineage, 1972 — the analog office layer; SD the high-volume iron; AR, from 1994, the digital cap-rock. Date any Sharp by its first letter. Within the SF-20xx bed the tail digits then declare speed — 2022 at 22, 2050 at 50 — stratigraphy with a bonus cipher.

Class IV — the enigmas

Some traffic is not meant to be read. Xerox ran overlapping series like agents on parallel covers: the 10 Series Marathons; the 50 Series, where 5018 means 18 cpm and 5028 means 28 right up until the 5090 means 135; then DocuTech, plainly named for its speed (135, 90, 180) the moment the office line stopped being decodable; then Document Centre, named for a mood. Océ defeats the department entirely: the 2400 runs 60 cpm, the 2500 runs 100; the digital 3165 of 1997 runs 62 while the analog 3100 of 1998 runs 100. Even the chronology decrypts wrong. We admire it, as one admires any unbroken code, from a distance.