I'll borrow a post written by Bill1954 to explain what logs is. Hope he does not mind.
"Log 10 is the use of logarithms to express viral load. If a number is expressed numerically, say, 1000,000, it can also be expressed logarithmically. The log 10 value of 1,000,000 = Log 6.0.
To figure a 1 log reduction, remove a zero from the right; to figure a 2 log 10 reduction, remove 2 zeros from the right;
1,000,000 = viral load
100,000 = 1 log reduction
10,000 = 2 log reduction
1,000 = 3 log reduction
100= 4 log reduction
Etc.
Good luck—
Bill"
http://www.medhelp.org/posts/show/733787?personal_page_id=5379&post_id=post_3868472
So if you have a decrease of viral load with 1 log during treatment, you have had a 90% decrease.
A 2 log decrease means a decrease of 99%.
A 3 log decrease means a decrease of 99.9%.
Etc.
You can use a scientific calculator to figure out what your viral load is in logs. You can find one on:
http://www.calculator.com/calcs/calc_sci.html
Just type in your viral load number and then press the key that says "log".
There is some variancy in the results of viral load tests. So half-a-log up or down really is no significant difference. The difference between your tests is a little more than that, 0.618 logs, but still not that much of a difference. My guess is that your actual viral load probably is somewhere between 20 million and 83 million.
It is not that hard to imagine that it is more important to know that one has gotten rid of 90% of the virus in one's body, rather than a number of international units per milliliter. That is why logs are more important than actual IU/ml.
Za