**HP 15C Collector's Edition: Some Thoughts and Hidden Modes**

On May 2, 2023, Moravia announced the return on the HP 15C programming scientific calculator. An initial limited run calculators were available that were delivered in July. Thankfully, another set of calculators will be available for order and delivery starting the end of September 2023.

Hopefully this will be true in future production runs, but in the initial run, the HP 15C came in a box, a Thank You card, with a leather case and a printed manual. I love the larger font and the clarity of the text of the Owner's Handbook. The handbook is an extension of the original HP 15C Manual along with an introduction from Wlodek Mier-Jedrzejowicz and Gene Wright.

You can download both the Manual and new edition of the Advanced Functions Handbook from the HP Calculator Literature website:

Manual: https://literature.hpcalc.org/items/2258

Advanced Functions Handbook: https://literature.hpcalc.org/items/2259

The compliment to Manual, the Advanced Functions Handbook goes into detail on several of the HP 15C's advanced features:

Solving Equations: The best ways for using the SOLVE command, and how the SOLVE feature finds roots of equations. This section also includes a section of finding the derivative (approximate slope) of a function and a financial time-value-of-money program.

Integration: The accuracy of the integral function and handling more difficult integral problems. In general, the accuracy and the time of integration is tied to the fixed decimal settings.

Complex Numbers: The internal workings of the complex mode (Flag 8), including solving equations and integrations.

Matrices: LU Decomposition, constructing identity matrices, and least-squares calculations.

**Programming: No More Pause Bug**

The PSE bug has been fixed! We can use the pause command to heart's content and the display won't flash off.

**Back of the Calculator**

The back of the HP 15C has a plate that has the following information: statistics registers, some conversions, a table of error, test, and matrix codes, how the ISG (increment skip if greater than) and DSE (decrement skip if equal) commands work, and the stack effects on several two-result commands.

**The Keyboard**

The battery compartment, which contains the two CR2032 batteries needed to power the HP 15C is held by a small screw. Thankfully, no special screwdriver is required, a small household or computer screwdriver should do the trick.

The keyboard, for me, is responsive. The keys give a nice, quiet click when they are pressed. I'm comfortable holding the calculator and letting my thumbs type on the keyboard efficiently.

**Hidden Modes**

Already, the HP 15C Collector's Edition has additional memory over the previous editions:

* A maximum of 99 memory registers, 78 uncommitted registers at default setting

* A maximum of 672 steps

We have some Easter Eggs on the HP 15C Collector's Edition. There are two hidden modes on the HP 15C:

HP 15.2 Mode: This mode ups the maximum of memory registers to 195, with 174 uncommitted registers at default setting. Pressing [ g ] ( MEM ) at the beginning will show "19174 00-0", as there really isn't enough room to display the total amount of uncommitted registers. I have my calculator in 15.2 mode and so far, this calculator works as well as the default HP 15 mode. Switching back to 15 mode will preserve as much memory as allowed, excessive memory will be lost.

HP 16 Mode: This modes accesses a possible-beta version of the HP 16C calculator. The HP 16C calculator was a popular computer programmer's calculator which emphasizes on bit manipulation, base conversions, and Boolean logic. I worked a little bit on this mode, and there was a few problems when working in decimal integer mode. More information on the HP 16C calculator here: https://www.hpmuseum.org/hp16.htm

How do we switch the hidden modes on the Collector's Edition?

1. With the calculator off: hold the [ g ], [ ENTER ], and [ ON ] keys. This gets the calculator into test mode.

2. Press [ 4 ]. Option 4 will not appear on the screen.

3. Set your mode:

* [ e^x ] for the original HP 15C Collector's Edition mode

* [ 1/x ] for the expanded 15.2 mode (not manufacturer supported)

* [ 7 ] for the HP 16C mode (not manufacturer supported)

Caution: The 15.2 and 16 modes are not manufactured supported. Enter at your own risk. For me, I have used the 15.2 mode and the calculator works fine. The original mode still has plenty of memory.

Discussion on the hidden modes starts about page 17 of this thread:

https://www.hpmuseum.org/forum/thread-19886-page-17.html

**Final Thoughts**

Welcome back, HP 15C! Knock on wood the HP 15C once again becomes mainstream like it's long time financial cousin the HP 12C.

Need help with RPN (Reverse Polish Notation)? Check out the RPN Programming tutorial series (which was done for the previous HP 15C Limited Edition) which starts here: http://edspi31415.blogspot.com/2011/11/hp-15c-programming-tutorial-part-1.html

Eddie

All original content copyright, © 2011-2023. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.