Easter Eggs for the HP-12C

[#1]

This one little device, the HP-12C Financial Calculator, has lasted 30 years and hasn’t really changed all that much. In fact, we ran a whole other story that explores the guts, the impact and the legacy of the HP-12C. You did read our story about one of the men behind the HP-12C calculator, Dennis Harms, right? Well, when I recently sat down with Dennis, he started telling me about some Easter egg tests that were built into the 12C. (And no, it’s not about having you type in “0.7734” on the keypad and turning it upside-down.) Want to learn a couple tricks that will make you the envy of your fellow nerds? Read on.

Dennis explains that as the calculators came off the assembly line, they had to be able to perform last-minute tests to make sure that everything worked. Here’s how they did it:

1. Start with the calculator off.
2. Push and hold the on key.
3. Push and hold one of the arithmetic keys on the right.
4. Release the on key
5. Release the arithmetic key

-The divide key does a display segment and keyboard test.  Press the keys in order across the top row, second row, etc.  Enter is pressed twice, once in the third row and once in the fourth row.  When this test is done the calculator comes up with the number, in this case “12”.   If there is a keyboard error or the keys are pushed in the wrong order, “Error 9” shows up.

-The multiply key runs a self-test on the ram and then lights all the display segments at once.

-The minus key does a memory reset and displays “Pr Error”.

-The plus key does a continuous self-test loop.  This is for a burn in test, i.e. a quality control test to see if a unit would over heat on continuous running.

According to Dennis, those functionality tests worked in the 12C Platinum (that launched in 2003) as well. Who knows? Maybe this will work on the new Limited Edition 12C that’s coming out now.

Darren Gladstone

Darren Gladstone (@Gizmogladstone) is a former journalist, now TNB's Blogger-in-Chief. He geeks out over games, gadgets and hot laptops.

[#2]

This works on my ancient HP 16C as well!

[#3]

My buddy Don noted:

Very interesting.  But not exactly "Easter Eggs" when the tests are explained in detail on pages 220-221 of the original HP-12C Owners Handbook.  Guess they figured that geeks like me would not have saved the documentation for 29 years.  My 12C was manufactured the 14th week of 1982 in the US.  How do I know?  At the time, all HP serial numbers (2214A01495 in my case) started with a format of yymmc - when and where it was made (hard to cheat warranty back then).  But the yy was actually the number of years after 1960 when they initiated the program.  And the c was which country A=America.  Since we did not have access to data bases instantly, it was necessary for the service reps to be able to determine when and where the unit was made for repair costs.  

I still have my HP 25 that I purchased in 1972.  And all the manuals.  And it still works great!

[#4]

Your buddy Don just earned some major nerd-cred bonus points there -- and if he actually deciphered the manufacturing date, double points! It's funny, people are coming out of the woodwork and telling me all their 12C stories.

[#5]

I started using the 12C while a mortgage broker here in San Jose.  I use it almost daily to add and subtract, divide and multiply.  I use to use it for amortization schedules, Loan payments, loan amounts, payments etc.  Return on investments and on and on and on.  What a beauiful Calculator.  It is THE best investment I have ever made.  the batteries last for ever as well.  Yes I still have the manuel and it still has plastic around it. (this is my second one, I use the old manuel)

Anyway.......HP..........Great job on a GREAT PRODUCT

Ron Keffer

[#6]

My 27-year-old 11c engineering calculator has the same tests.  They are documented on pages 234 and 235 of the original manual.  My 11c receives daily use, and the only thing I've replaced in 27 years are the batteries -- perhaps four or five times in total.  They last a very long time.