Let me see if I can remember this.  It is basically an impedence match, so
a two to one would mean the  impedance is 50 ohms over 25 ohhms reverse or
100 ohms over 50 ohms.  Now, let us say we are reading the power in watts
and we want to calculate the swr.  I wrote a program to do this once.  Let
us say you read 100 watts forward and ten watts reflected.  As I recall,
you take square root of forward plus square root of reflected and divide
this answer by square root of forward minus square root of reflected.  So,
in this example, suqare forward is ten, and square root of ten is 3.16, so
we add 10 plus 3.16 twhich is 13.16.  Now take ten minus 3.16 which is
6.84.    Now the final step is 13.16 over 6.84 equals 1.923, so the wr is
1.923 to one.

Hope this makes sense.  As I said in an earlier post, 1.5 is aprox 6
percent and two to 1 is 11 percent.
73s
Butch Bussen
wa0vjr