Versions, Care, Collecting and the Exam Room

A 12C rarely needs more than fresh batteries. This volume covers telling one 12C from another, keeping one working, what they cost, and the professional exams for which the 12C is one of only two calculators allowed.

8.1 Telling them apart

Every 12C has the same keyboard, so the clues are on the outside of the case and inside the battery door:

Table 1 — Every 12C has the same keyboard, so the clues are on the outside of the case and inside the battery door

Clue	What it means
a small door over three LR44 cells	an original Nut-processor 12C, 1981–2001
one CR2032	a 12C made from 2001 to 2008 (from serial CN11500001)
two CR2032	an ARM-based 12C, 2008 or later
”30th Anniversary Edition” on the bezel and back	the 2011 edition, with its own production number
”HEWLETT·PACKARD” across the faceplate	made before 2022
no “Hewlett-Packard”, a screw on the battery door	made for HP by Moravia or Royal, 2022 or later; mine
silver face, algebraic mode keys	a 12C Platinum, a different machine (volume 4)

Older 12Cs carry a serial number on the back in HP’s format of the time, yywwCnnnnn: years since 1960, the week, a letter for the country, and the unit number. A serial such as 2835A37379, a 12C in the Computer History Museum, reads as 1988, week 35, made in the USA (A); B is Brazil, S Singapore and later CN China and MY Malaysia. The newest calculators carry a lot number instead, such as mine, 9CJ251, whose meaning HP has not published (volume 1).

Collectors notice small differences between batches, down to the keys: one photograph on Wikimedia Commons is of a 12C whose y^x key shows an SST legend beneath it.

8.2 Batteries

HP’s guide for the two-cell 12C gives the rule that matters most: “To prevent memory loss, never remove two old batteries at the same time. Be sure to remove and replace the batteries one at a time.” (p. 193). The procedure (pp. 193–194):

1. Turn the calculator off. On a 2022 or later 12C like mine, undo the screw, then slide off the battery cover.
2. Remove one old CR2032 and fit a new one, its + side facing outward; then do the same with the other.
3. Do not press any keys while a battery is out, or the memory “may be lost”.
4. Turn it on. Pr Error means the memory has been lost; any key clears it, and programs and registers must be re-entered.

HP warns against rechargeable cells. A low battery shows as a battery symbol at the top left of the display; when it flashes, the cells should be changed soon.

8.3 Faults

The 12C is famously durable: Finseth’s database notes that “no matter how hard they try, they just can’t kill it”, and the Corvallis Gazette-Times reported in 2006 that one had survived a fall from a desk onto concrete. When something does go wrong:

• Missed or doubled key presses: check the batteries first; on older units, dust under the key contacts.
• Odd behaviour after a drop or a power cut: the memory can reset itself (p. 70). Holding − while pressing ON clears it deliberately.
• A dead display segment: run the ON ÷ keyboard and display test (volume 6). A single segment missing is the display itself, which can only be replaced; several missing may be a contact between the display and the board.
• Opening the case: older Voyagers come apart through screws under the rubber feet. The newest are held together by heat-staked plastic pins; one repairer who opened one by removing all 41 found the keys loose afterwards. A modern 12C that fails is cheaper to replace than to repair.

For cleaning, HP’s guide gives no advice; a cloth barely damp with water, kept off the printed legends, is the safe course.

8.4 What they cost

Table 2 — What they cost

When	What	Price
September 1981	HP-12C, new	$150
1986	HP-12C	$99
January 2003	HP-12C	$69.99
August 2011	30th Anniversary Edition	$79.99 (€129 in the Netherlands)
about 2023	HP-12C, HP’s online store	$49.99
2025–26	HP-12C, new, Amazon	about $37 to $48
2026	12C Gold, Brazil	R$290 to R$540

Because the 12C has never gone out of production, ordinary used ones are cheap: forum reports put boxed 1980s calculators at $30 to $50. What adds value, by collectors’ accounts, is an early US-made calculator with its box, case and manual, for the anniversary editions, and for the HP-80 and the other financial calculators of the 1970s. Beware of eBay listings of “30th Anniversary” calculators that show an ordinary 12C: the real thing says so on the bezel and the back.

8.5 Clones and the rogue firmware

The 12C’s imitators (volume 3) are sold under their own names and are easy to tell apart. The one real trap was the batch of 12Cs sold in Brazil in 2023–24 with firmware dated March 2023 that gave slightly wrong answers. A genuine 12C can be checked three ways: it switches to a decimal comma when switched on with the . key held down; its ON × self-test ends in −8,8,8,8,8,8,8,8,8,8; and on Duncan Murray’s “penny a second” problem (volume 5) it gives 331,667.0067 or very close.

8.6 The exam room

The 12C’s most important use today may be in the examinations of the finance profession, most of which allow only a handful of calculators:

Table 3 — The 12C's most important use today may be in the examinations of the finance profession, most of which allow only a handful of calculators

Exam	12C allowed?	Rule
CFA (Chartered Financial Analyst)	yes	”Only two calculator models are authorized for use during CFA® Program exams”: the TI BA II Plus and Professional, and the “Hewlett Packard 12C (including the HP 12C Platinum, 12C Platinum 25th anniversary edition, 12C 30th anniversary edition, and HP 12C Prestige)“
FRM (GARP)	yes	the 12C family, the BA II Plus family, and HP’s 10B II, 10BII+ and 20B; with any other, “their Exam will not be graded”
CAIA	yes	the same two families as the CFA
CFP Board	yes	a list including the HP 12c and 12c Platinum; notes or formulas printed on a calculator must, by reports of the full policy, be covered
SOA actuarial exams	no	Texas Instruments models only
FINRA (Series 7 and others)	no	only the calculator the test centre provides

So my 12C, as an ordinary “HP 12C”, is allowed in the CFA, FRM and CAIA exams. The CFP Board’s rule about printed notes is a reminder that the label on its back is, strictly, a crib sheet. The CFA Institute also publishes a guide for candidates to both of its permitted calculators, which is in the Library.

8.7 The documents in the Library

Everything in the Reference Library for this series:

• My calculator: HP’s HP 12c financial calculator user’s guide, Edition 5 (2008); the Owner’s Handbook and Problem-Solving Guide (1992); the Quick Start Guide (2008); the Solutions Handbook (1987); the Training Guide (1984); and the 12C Platinum Owner’s Handbook (2003).
• Before the 12C: the HP-80 Owner’s Handbook and problems booklet; the Hewlett-Packard Journal of May 1973 (HP-80); the HP-92 Owner’s Handbook and the Journal of October 1977 (HP-92).
• Inside: HP’s HP-41 IC specifications (the Nut processor) and Atmel’s AT91SAM7L128 datasheet (the 2008 ARM chip).
• Patents: US 3,863,060, US 3,946,218 and US 3,955,074 (HP-80); US 4,055,757 (BEGIN/END); US 4,430,531 (Voyager keyboard).
• Rivals and exams: TI’s BA II Plus Guidebook; the CFA Institute’s guide to the BA II Plus and HP 12C.

8.8 Gaps

HP has published nothing on the 12C’s hardware or on its lot numbers, so the chip in my calculator and its date of manufacture rest on collectors’ work. The 12C’s own interest-rate algorithm is undocumented. The original Nut clock speed is disputed. No sales figure has been published since 2006. No 12C made in Japan has been confirmed, and the HP-80’s sales are unknown.

Sources

• HP, HP 12c financial calculator user’s guide, Edition 5 (2008), pp. 70, 193–195; Edition 4 (2005).
• Wikipedia, “HP-12C”; Finseth, HPDATAbase (“HP-12C”, serial numbers); Computer History Museum, HP-12C X1427.97; Museum of HP Calculators forum on repairs, versions, prices and fake anniversary editions.
• Prices: Finseth; VentureBeat and id.nl (2011); Benzinga (2023); camelcamelcamel (Amazon); Buscapé and KaBuM (Brazil).
• The Register, 21 September 2024; Duncan Murray, “HP-12C comma” (2024).
• CFA Institute, calculator policy (updated 12 January 2026); GARP, FRM exam policies; CAIA Association, calculator policy (7 April 2025); CFP Board, “What to bring to the exam”; Society of Actuaries, calculator list; FINRA, Series 4 outline.