HP Calculators with native C-F temperature conversion

[C.Ret]

(02-10-2024 11:25 AM)calc-calcs Wrote:  Is the HP-55 the only pre-80s calculator that does C->F/F->C temperature conversions natively?

No. There certainly where a few other calculators that does °C↔°F conversion at the time.
I'm far from knowing them all.

But, for example, the Texas Instruments Ti-59 or Ti-58 were all available with the Main Library solid state module which ML-25 Unit Conversion (2) program allows volume, weight and temperature conversions.

   

(02-10-2024 11:25 AM)calc-calcs Wrote:  Could the HP-41 (or any other model) made to have this conversion with an add-on module?

Yes, most definitely and also without any add-on module as well. Like all programmable calculators of this era.
The high-end calculators of the time were programmable to meet the specific needs of their users. Temperature conversions are a typical example of use. These conversions can simply be programmed directly into these machines.

What's special about the HP-41 is that with a few instructions a program can be composed to offer all conversions between degrees Kelvin, Fahrenheit and Celcius in a user-friendly and intuitive environment:

001 LBL"TCONV" 
002  273.15  STO 00  SF 27  "A:.F B:.K C:.C"  PROMPT
007  LBL A  FC?C 22 XEQ 01  XEQ 00  SF 01  STO 01  FIX 1  "F"  XEQ 10
016  LBL B  FC?C 22 XEQ 02  XEQ 00  SF 02  STO 02  FIX 2  "K"  XEQ 10
025  LBL C  FC?C 22 XEQ 03  XEQ 00  SF 03  STO 03  FIX 1  "C"  XEQ 10  GTO A 

035   LBL 00  CF 01  CF 02  CF 03  RTN
040   LBL 01  FC?C 02 XEQ 02  RCL 00  -  9  *  5  /  32  +  RTN
052   LBL 02  FC?C 03 XEQ 03  RCL 00  +  RTN
058   LBL 03  FC?C 01 XEQ 01  32  –  5  *  9  /  RTN

068   LBL 10  ASTO L  CLA  ARCL X  "~ ."  ARCL L  FIX 4  PROMPT  CF 22
077 END

Usage:
Initialize the program by executing XEQ “TCONV”
Enter a temperature and press A, B or C to indicate respectively whether it is Fahrenheit, Kelvin or Celsius.
To convert the displayed temperature, press A, B or C (without entering a value) to obtain °F, °K or °C respectively.

The displayed temperatures are stored in registers R01, R02 and R03 depending on whether they are °F, °K or °C.
The result of the conversion is in the X register.
The ALPHA register gives the rounded value followed by its unit.
Pressing R/S key cycle through the three units.

Ultimately this is how I like to have the conversions on my HP-41.
Don't hesitate to create your own method. This is the main purpose of the HP-41 which is designed to be customized by the user.

If you don't believe me, just have a look under the display at the message written on the four largest keys this machine has: ON any USER press the PRGM is ALPHA.