TI-84 Plus CE, HP 15C, and HP 12C: Decoding the Gradematic 100
GPA as a function of grade
Last December, we have gave a spotlight on the Calculated Industries 100 from 1983. The Gradematic 100 was a specialty calculator that determines the GPA average for a student or a bunch of students in a class. We can either use numerical grades, where the maximum total score and the minimum passing grade (better than E (or F)) are set, or letter grades, where the letters are given an approximated. To see the review, click the link below:
https://edspi31415.blogspot.com/2025/12/spotlight-calculated-industries.html
Using the standard grade scale for a single assignment, with a perfect score being 100 and the minimum passing grade is 60, the following scores are given the GPA:
GRADE (0 – 100) |
GPA |
Letter Grade Given by Gradematic 100 |
0 |
0.00 |
E (can stand for F) |
10 |
0.08 |
E (can stand for F) |
20 |
0.16 |
E (can stand for F) |
30 |
0.25 |
E (can stand for F) |
40 |
0.33 |
E (can stand for F) |
50 |
0.41 |
E (can stand for F) |
55 |
0.45 |
E (can stand for F) |
60 |
0.50 |
D- |
65 |
1.00 |
D |
70 |
1.50 |
C- |
75 |
2.00 |
C |
80 |
2.50 |
B- |
85 |
3.00 |
B |
90 |
3.50 |
A- |
95 |
4.00 |
A |
100 |
4.50 |
A+ |
Plot of values (using a TI-84 Plus CE):
As we can see, the plot consists of two line segments: one where grades value from 0 to 60, and one where grades value from 60 and higher. It is apparent that that the two parts makes a piece-wise function consisting of two lines.
Note: the graphs and statistics were done with the TI-84 Plus CE Python (will work with any TI-84 CE family). The piecewise function is from the math-math menu.
The Gradematic 100 distributes the GPA as:
E: 0.00 (or F) |
D+: 1.33 |
C+: 2.33 |
B+: 3.33 |
A+: 4.33 |
D-: 0.66 |
C-: 1.66 |
B-: 2.66 |
A-: 3.66 |
|
D: 1.00 |
C: 2.00 |
B: 3.00 |
A: 4.00 |
|
Note: The distributed GPA scales will vary among the school districts and systems. However, we will assume the system that matches the default 60/100 system.
HP 15C and HP 12C: Find the GPA given numeric grade
HP 15C Code:
LBL C |
001 |
42, 21, 13 |
6 |
002 |
6 |
0 |
003 |
0 |
x≤y |
004 |
43, 10 |
GTO 1 |
005 |
22, 1 |
2 |
006 |
2 |
× |
007 |
20 |
÷ |
008 |
10 |
RTN |
009 |
43, 32 |
LBL 1 |
010 |
42, 21, 1 |
CL x |
011 |
43, 35 |
1 |
012 |
1 |
0 |
013 |
0 |
÷ |
014 |
10 |
5 |
015 |
5 |
. |
016 |
48 |
5 |
017 |
5 |
- |
018 |
30 |
RTN |
019 |
43, 32 |
HP 12C Code:
6 |
01 |
6 |
0 |
02 |
0 |
x≤y |
03 |
43, 34 |
GTO 09 |
04 |
43, 33, 09 |
2 |
05 |
2 |
× |
06 |
20 |
÷ |
07 |
10 |
GTO 00 |
08 |
43, 33, 00 |
CL x |
09 |
35 |
1 |
10 |
1 |
0 |
11 |
0 |
÷ |
12 |
10 |
5 |
13 |
5 |
. |
14 |
48 |
5 |
15 |
5 |
- |
16 |
30 |
GTO 00 |
17 |
43, 33, 00 |
Eddie
All original content copyright, © 2011-2026. 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.
