What is mean by log10 redution? Suppose, initial count was 10^4 and on 14th day we get 10^ 2 then how much log reduction is observed?

Please give detail explanation for log calculation along with example

Dear

shall be reading the chapter USP 51 in USP theirs no found log 10 in this chapter and this is the means of log reduction

1 log reduction = 90% reduction|

2 log reduction = 99% reduction|

3 log reduction = 99.9% reduction|

4 log reduction = 99.99% reduction|

5 log reduction = 99.999% reduction|

6 log reduction = 99.9999% reduction|

Thanks and Regards

Mohamed Ezz