converting currency pairs

 
This is a hard one to explain, but here goes: (think celcius - Fahrenheit)
there are two currencies that exactly mirror each other..
one is on a scale of about half of the other, and moves perhaps 3 pips for every 2 pips the other currency moves. The question is, how would you make a scale so that you could look at one currency price and calculate the other currency price?
hope someone can help with this, I am deadended because of it.
 
you can estimate a coefficient by dividing one currency into the other and creating a moving average of that.

for(i=0;i<period;i++)
sum+=xxx[i]/yyy[i];
coeff=sum/period;
 
hmmmmm interesting idea... but.... i am afraid that the moving average will not have a "base".
if one currency changes faster than the other, the average will do funny things i think , like if both go up, the average might actually go down.. ... i will look at this and try to get back to you..
(run it up the old tester pole and see if anyone salutes)
 
ah, no luck.. the pair changes differently over time, like trying to calculate degrees F to C when each month F changes from 32 -212 to 22 -300 etc.. no way to keep up with it..
Reason: