HP · 00041-15003
When the HP-41C arrived in 1979, its built-in functions stopped short of integration, root finding, matrices and complex numbers. The Math Pac filled the gap the day the calculator launched. Plug it in and you get a library of programs: matrix work up to 14 by 14, solving equations, polynomial roots, integration, differential equations by Runge-Kutta, Fourier series, complex arithmetic, triangle solutions and coordinate transformations. Each one prompts you in words on the 41's display. HP revised the ROM twice, to revisions B and C. It's one of the most useful pacs for an engineer's 41, and the manual matters as much as the module, since it explains the inputs each program expects.
Module check
Should come with it
HP
RPN programmable$200–$400 typical ask
HP
RPN programmable$190–$290 typical ask
HP
RPN programmable$280–$460 typical ask
The module's contacts are the thing to check: corrosion from a 41's leaked batteries can reach them. A pac without its manual is harder to use, since each program has its own inputs.
Choosing modules for a 41? The HP-41C, CV and CX explainer covers memory, ports and what each model has built in.
Buying guide
We'd buy night_owl_items' Math Pac titled works at $43 delivered, since the photo shows the manual, two overlays and the reference cards with the module, and the manual is what tells you the inputs each program expects. There are at least 14 for sale, bare modules ask $21-49 delivered, and jones.sebago.lake's set titled complete in box asks $61. It fits every HP-41, though on a 41C with memory modules it has to sit in a higher-numbered port than the memory. Ask for a close photo into the module's open end, since corrosion from a leaky 41 can reach the contacts, and check the label says Math I, because the part number printed under it varies from listing to listing.
$20.99delivered
The lowest price on a Math Pac at $21 with free shipping, from a 99.8% seller. It's the module alone with no manual and no test claim, so ask for a close photo of the contacts.
Hewlett Packard HP Math I Pac Module HP 5061-5261 for 41C/41CV/41CX Calculators
$43.00est. delivered
Titled works, and the photo shows the manual, two overlays and the reference cards with the module, at $43 delivered from a 100% seller. That's the whole kit for about what bare modules ask.
HP-41C Mathematics Pac Module 00041-15019 for HP 41C Calculator, MATH I, works
$43.00est. delivered
The only listing here titled working, and it has the manual that explains each program's inputs. Plug it in and its programs should show up in CATALOG 2.
HP-41C Mathematics Pac Module 00041-15019 for HP 41C Calculator, MATH I, works
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$20.99delivered
$20.99 · free shipping
Buy It Now$20.99
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
Module only, no manual. No test claim.
Seller: sshebalee1982
99.8% positive
Used$43.00est. delivered
$38.00 + $5.00 shipping
Buy It Now$38.00
Good buy
Titled works. Manual, overlays and reference cards in the photo.
Seller: night_owl_items
100% positive
Used$27.49est. delivered
$21.99 + $5.50 shipping
Buy It Now$21.99
Our take
Module only, titled 5061-5261. No test claim.
Seller: miller1987
100% positive
Used$40.00est. delivered
$27.50 + $12.50 shipping
Buy It Now$27.50
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
Module with one overlay. No manual named.
Seller: husmus
100% positive
Used$40.99delivered
$40.99 · free shipping
Buy It Now$40.99
Our take
Module only, 00041-14002 label in the photo. No test claim.
Seller: tech_revived
99.9% positive
Used$43.14est. delivered
$34.95 + $8.19 shipping
Buy It Now$34.95
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
Manual, reference card and overlay in the photo. No test claim.
Seller: jtomaha
100% positive
Used$61.26est. delivered
$44.41 + $16.85 shipping
Buy It Now$44.41
Our take
Titled complete in box; the photo shows the pac box.
Seller: jones.sebago.lake
99.8% positive
Used$42.82est. delivered
$35.00 + $7.82 shipping
Buy It Now$35.00
Check the seller
Module only. Seller feedback 88.9%.
Seller: anova11
88.9% positive
Prices change daily. The live eBay search shows everything listed now, including anything new since Oct 15, 2026.
See every listing on eBay ↗eBay searchHP
Module$30–$65 typical ask
HP
Module$80–$120 typical ask
HP
Module$140–$190 typical ask