**RPN 1250: One of a Kind (HHC 2018)**

RPN 1250 |

**Introduction**

The RPN 1250 is a re-purposed Texas Instruments TI-1250 calculator by Beniot Maag. Maag has previously re-purposed the Texas Instruments TI-1200 into the RPN 1200. Nothing short of marvelous.

The RPN 1250 has been Maag’s project since 2016. He posted a thread on the MoHPC’s website: http://www.hpmuseum.org/forum/thread-4819.html

I won the RPN 1250 as one of the door prizes at HHC 2018. You can read my summary here: http://edspi31415.blogspot.com/2018/10/hhc-2018-in-review.html

The RPN 1250 is powered by a V9 volt battery.**Features**

The RPN 1250 has 24 keys. Each key, except one, has a primary function with two shifted functions. The shift key, labeled [ F/G ], is a dual shift key. Press [ F/G ] once for the first shifted functions (in yellow), twice for the second shift functions (in blue), and three times recycle to the original function.

**Update: The RPN 1250 has 24 keys, not 40. (10/13/2018)**

The functions include: trigonometry, logarithmic, exponential, integer part, fraction part, reciprocal, roots, and powers. Four sets of conversions are included: in/mm, mi/km, lb/kg, and °C/°F.

The angle for the trigonometric functions are in radians. There is a convert to radians function.

The display is 7 digits or 4 with 2 digit exponents, with the default mode is FIX 2 (2 decimal places). However, the largest number the RPN 1250 can handle is 3.40 * 10^38.

**The Escape Mode**

The escape mode allowed the use to show what version of firmware, adjust the brightness of the LCD display and execute display tests.

**Programming**

The RPN 1250 has RPN keystroke programming. There are 20 registers (0-9 and .0 (dot 0) through .9 (dot 9)). Store and recall arithmetic are available. Stack contents are accessible, along with an indirect addresses through the [ENTER] key.

There are 20 labels available (0 to 9 and .0 to .9). On the surface, the memory is volatile. However, the RPN 1250 has three permanent slots that we can store the program space into three slots.

There are twelve tests that called by the TST function: x = 0, x ≠ 0, x > 0, x ≥ 0, x < 0, x ≤ 0, x = y, x ≠ y, x > y, x ≥ y, x < y, and x ≤ y.

Each step in the program is shown by the step and the command pressed. Displaying the command proved to be a challenge for Maag, since he only had seven segment characters to work with.

The program space is 98 steps. The programming works well and is a pleasure to use. The thing I have to get used to is the having to press the shift key two times for the second shifted functions.

Let’s take a look at few sample programs.

Each program has input and output rounded to 2 decimal places.

**RPN 1250 Program: Area of the Circle**

1 LBL 0

2 x^2

3 π

4 *

5 RTN

Examples:

Input: 5.00, Output: 78.54

Input: 10.00, Output: 314.56

Input: 28.00, Output: 2463.01

**RPN 1250 Program: Sign Function**

1 LBL 1

2 ENTER

3 x^2

4 √

5 ÷

6 RTN

Examples:

Input: -54.00, Output: -1.00

Input: 38.00, Output: 1.00

Input: 0.00, Output: dt Error

**RPN 1250 Program: Hypothesis**

1 LBL 2

2 x^2

3 x<>y

4 x^2

5 +

6 √

7 RTN

Examples:

Input: 3.00, 4.00, Output: 5.00

Input: 5.00, 8.00, Output: 9.43

Input: 19.00, 11.00, Output: 21.95

**RPN 1250 Program: Sine of a Angle in Hours-Minutes (format HH.MM°)**

1 LBL 3

2 ENTER

3 IP (INT)

4 x<>y

5 FP (FRC)

6 1

7 0

8 *

9 6

10 ÷

11 +

12 →RAD

13 SIN

14 RTN

Examples:

Input: 40°50′, Output: 0.65

Input: 20°13′, Output: 0.35

**RPN 1250 Program: Quadratic Equation (x^2 + b*x + c = 0)**

Store b in R1 and c in R2. Run the program. You get the discriminant.

Discriminant is negative: next two results is the real and imaginary part of the complex conjugate roots

Discriminant is non-negative: the next two results are the real roots

1 LBL 0

2 RCL 1

3 x^2

4 RCL 2

5 4

6 *

7 –

8 STO 3

9 R/S

10 TST 1 (x

11 GTO 8

12 RCL 1 (real roots)

13 CHS

14 RCL 3

15 √

16 +

17 2

18 ÷

19 R/S

20 RCL 1

21 CHS

22 RCL 3

23 √

24 –

25 2

26 ÷

27 RTN

28 LBL 8 (complex roots)

29 RCL 1

30 CHS

31 2

32 ÷

33 R/S

34 RCL 3

35 x^2

36 √

37 √

38 2

39 ÷

40 RTN

Examples:

Input: R1 = 8, R2 = 3; Output: Discriminant: 52.00, Root 1: -0.39, Root 2: -7.61

Input: R1 = 6, R2 = 11; Output: Discriminant: -8.00, Real: -3.00, Imag: 1.41 (-3.00 ± 1.41i)

Thank you Benoit Maag, this calculator is truly one of the kind!

Eddie

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