The Museum of HP Calculators

Area of a Polygon for the HP-55

This program is Copyright © 1975 by Hewlett-Packard and is used here by permission. This program was originally published in "HP-55 Mathematics Programs".

This program is supplied without representation or warranty of any kind. Hewlett-Packard Company and The Museum of HP Calculators therefore assume no responsibility and shall have no liability, consequential or otherwise, of any kind arising from the use of this program material or any part thereof.

Overview

If the x-y coordinates of the vertices of a polygon are known, the area can be found by the following formula:

Area = 0.5 * [(x1 + x2)(y1 - y2) + (x2 + x3)(y2 - y3) + . . . + (xn + x1)(yn - y1)]

Traverse the coordinates clockwise for a positive area.

Instructions

Step Instructions Input Data/Units Keys Output Data/Units
1 Enter program      
2 Input (x1, y1) x1* ENTER↑  
    y1* BST R/S 0.0
3 Input (xi, yi) for i = 2, . . ., n xi ENTER↑  
    yi R/S intermediate
4 Input (x1, y1) again x1 ENTER↑  
    y1 R/S Area
   * if x1 & y1 are complicated      
  you can store them in R6 and      
  R7 for step 4.      

Example

For a polygon with the points (1,3), (2,4), (5,4), (5,7) (7,5), (7,1), (3,1), the area would be 19.50.

The Program

LINE CODE KEYS
00.
01.   33  STO
02.   02  2
03.   23  R↓
04.   33  STO
05.   01  1
06.   00  0
07.   33  STO
08.   05  5
09.   84  R/S
10.   33  STO
11.   04  4
12.   23  R↓
13.   33  STO
14.   03  3
15.   34  RCL
16.   01  1
17.   61  +
18.   34  RCL
19.   02  2
20.   34  RCL
21.   04  4
22.   51  -
23.   71  x
24.   02  2
25.   81  ÷
26.   33  STO
27.   61  +
28.   05  5
29.   34  RCL
30.   04  4
31.   33  STO
32.   02  2
33.   34  RCL
34.   03  3
35.   33  STO
36.   01  1
37.   34  RCL
38.   05  5
39.  -09  GTO 09

Register Use

R1  xi-1
R2  yi-1
R3  xi
R4  yi
R5  area

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