HP · RPN scientific · October 1988 to 1995
When the HP-42S arrived on October 31, 1988, it looked like HP's answer to the HP-41: it runs 41 programs, and its two-line display shows menus over the soft keys. It had no ports or card reader, though, so HP sold it as a successor to the 15C instead. Inside its 8 KB are matrices with an editor, complex numbers, a solver, integration, base conversion and even program-driven graphics, all in a pocket-sized Pioneer body that runs well over a year on three button cells. It was made until 1995. Its reputation outlived it: Thomas Okken's Free42 rewrote its software from scratch, and SwissMicros sells the DM42, a modern calculator built around Free42.
Good forEngineeringCollecting
Bench check
Should come with it
Check the listing photos against this list, and ask the seller about anything you can’t see. A missing piece should come off the price.
Few documented faults. Check for leaked button cells, dust behind the display, and run the built-in self-test.
New to old calculators? The condition checklist covers battery corrosion, displays, keys and card readers, and RPN in one hour gets you typing on an HP.
Buying guide
We'd buy the 42S titled tested with a case at $187 delivered, just under the $190-260 band most working ones ask. There are at least 19 for sale, mostly in the US with a few from Canada, and the one titled mint with its manual asks $390, about 1.8 times the $214 median. Ask the seller to run the self-test from the owner's manual, which should end with OK-42S, and for a photo with the battery door off to check for leaked button cells. A steel case with a USB port is a SwissMicros DM42, a modern clone, not an HP.
$150.00delivered
The lowest delivered 42S at $150, titled tested with a battery, and the photo shows it switched on. There's no case, and the 1987 in the title predates the 42S, so ask for the self-test result.
Hewlett Packard HP 42S RPN Scientific Calculator Vintage 1987 w/ Battery Tested
$186.82est. delivered
Titled tested with a case, at $187 delivered from a 100% US seller, just under the band. Ask for the OK-42S self-test screen and a look in the battery compartment.
HP 42S RPN Scientific Programmable Calculator Hewlett Packard Tested With Case
$199.99delivered
Titled tested and working with three new Energizer cells, at $200 delivered with free shipping. Fresh batteries mean nothing to sort out before you start.
HP-42S Scientific w/(3) new Energizer batteries. Tested and working.
Delivered prices include shipping as eBay quoted it to a US address on Oct 15, 2026. Many sellers charge by distance, so your total may differ. eBay shows yours before you pay.
Snapshot
Checked . Some may have sold.
Delivered prices include shipping as eBay quoted it to a US address on Oct 15, 2026. Many sellers charge by distance, so your total may differ. eBay shows yours before you pay.
Used$150.00delivered
$150.00 · free shipping
Buy It Now$150.00
Good buy
Titled tested, with a battery. Photo shows it on; the 1987 in the title predates the 42S.
Seller: shadow338
100% positive
Used$186.82est. delivered
$180.00 + $6.82 shipping
Buy It Now$180.00
Good buy
Titled tested, with a case.
Seller: lifeisswell
100% positive
Used$199.99delivered
$199.99 · free shipping
Buy It Now$199.99
This seller takes offers, and many sellers accept less than the asking price.
Fine if you might miss it? Send an offer first. Someone else can still buy it while you wait for a reply.
Want it for sure? Use Buy It Now.
Good buy
Titled tested and working, with three new Energizer cells.
Seller: greatsurplusdeals
100% positive
Used$186.12est. delivered
$168.56 + $17.56 shipping
Buy It Now$168.56
This seller takes offers, and many sellers accept less than the asking price.
Fine if you might miss it? Send an offer first. Someone else can still buy it while you wait for a reply.
Want it for sure? Use Buy It Now.
Our take
Titled tested and working with a new battery. Ships from Canada, and the photo shows only the back.
Seller: zwanemwaikambo
100% positive
Used$213.02est. delivered
$200.00 + $13.02 shipping
Buy It Now$200.00
This seller takes offers, and many sellers accept less than the asking price.
Fine if you might miss it? Send an offer first. Someone else can still buy it while you wait for a reply.
Want it for sure? Use Buy It Now.
Our take
Titled tested, with the owner's manual in the photo.
Seller: suzq
100% positive
Used$221.79est. delivered
$210.70 + $11.09 shipping
Buy It Now$210.70
Our take
With a case, shown switched on. No test claim. Ships from Canada.
Seller: vintagesterlingfinds
100% positive
Used$307.51est. delivered
$299.00 + $8.51 shipping
Buy It Now$299.00
Check the seller
Titled with a case, but seller feedback is 95.5%.
Seller: kobel-co
95.5% positive
Used$390.00delivered
$390.00 · free shipping
Buy It Now$390.00
This seller takes offers, and many sellers accept less than the asking price.
Fine if you might miss it? Send an offer first. Someone else can still buy it while you wait for a reply.
Want it for sure? Use Buy It Now.
Priced high
Titled mint, with the manual. About 1.8 times the median.
Seller: makila138-158
99.4% positive
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