ParREq Documentation
--------------------

By Larry McElhiney

Parallel Resistor Calculator (Rev 1.2)

The following HP48 program which finds parallel resistance elements 
will be useful for both electronics technicians and hobbyests. 

USE:  Put the value of the resistance you want on the stack and press 
PARAL (softkey 'A' in the 'CST' menu). PARAL presents a list of values 
(standard 1%) which when paralleled will yield the desired value. The 
accuracy of each combination is also displayed. The required accuracy 
is specified by the variable ACCU.  The soft key ACCUR ('B') stores 
and retrieves this accuracy variable. 

Pressing any key while PARAL is running will advance the display to 
the next 'page' of values. The previous 'page' may be displayed by 
pressing the soft key PREV ('E'). The program may be exited by 
pressing softkey QUIT ('F'). Note that the soft key functions will not 
be visible during the execution of the program but will continue to 
function normally. 

THEORY:  PARAL uses an equation derived with the HP48 from a list of 
valid 1% values.  This list was created using the formula 

            INV(96)
    X = X*10        for all values between 1 ohm and 1 G ohm

                                0.0239852613838*X
The HP48 found  0.976300098965*e                  

This equation and its inverse form the basis of PARAL. When X is any
integer a unique one percent value will be found. The values created 
with this equation must then be rounded to 3 digits in order to 
represent the standard one percent value set. The inverse of this 
equation creates n 'bins' which, when integer, represent the nth one 
percent value.    

PARAL is accurate to at least 4 decimal places for all values 
from 1 ohm to 9.76E499 ohms (now that's a big resistor *:-)). 

--
Larry L. Hoppis         PO Box 472, Mt. Hermon, CA  95041  USA
