Call Centre Calculator for the HP-25

This program is by Bill Harrington and is used here by permission.

This program is supplied without representation or warranty of any kind. Bill Harrington 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

The goal of this program is to calculate the number of call centre agents required to meet a specific level of service. It is intended to answer questions in the form: "How many agents do I need if I get 431 calls during my busiest hour, where a typical call lasts for 51 seconds and I want my customers to queue for no more than 40 seconds, 80% of the time?".

The calculation is made using the Erlang C equation which give the probability that a caller will have to wait for an agent:

Where:
Pc is the probability that a customer will experience a non zero delay in talking to an agent
E is the total traffic offered (in Erlangs)
N is the total number of agents available

Listing

LINE    CODE    KEYS
 00
 01         1   1
 02   23 51 6   STO + 6
 03      24 3   RCL 3
 04      24 6   RCL 6
 05      14 3   yx
 06      24 6   RCL 6
 07        31   ENTER↑
 08        31   ENTER↑
 09         1   1
 10        41   - 
 11     15 71   x=0
 12     13 16   GTO 16
 13        61   ×
 14     14 73   Last x
 15     13 09   GTO 09
 16        22   R↓
 17        71   ÷
 18  23 51  5   STO + 5
 19     24  5   RCL 5
 20        71   ÷
 21     23  7   STO 7
 22     24  6   RCL 6
 23        61   ×
 24     24  6   RCL 6
 25     24  3   RCL 3
 26        41   -
 27     24  3   RCL 3 
 28     24  7   RCL 7 
 29        61   ×  
 30        51   + 
 31        71   ÷
 32     23  4   STO 4
 33     24  3   RCL 3
 34     24  6   RCL 6
 35        41   -
 36     24  1   RCL 1
 37        61   ×  
 38     24  0   RCL 0
 39        71   ÷
 40     15  1   ex
 41        61   ×  
 42        32   CHS
 43         1   1
 44        51   +
 45     24  2   RCL 2
 46     14 51   x>y
 47     13 01   GTO 01
 48     24  6   RCL 6
 49     13 00   GTO 00

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