Natural logarithm of quotient of two equal numbers

Questions
1

Hello! I’m using Mathematica 9.0.0.0 and I’ve come across following puzzling results:

In[12]:= Log[8.62096/8.62096]
Log[8.62097/8.62097]
Log[8.62098/8.62098]

Out[12]= 0.

Out[13]= -1.11022*10^-16

Out[14]= 0.

When I calculate logarithm of quotient of two equal numbers I do not always get zero. What might be the reason for that?

2

The second logarithm’s argument is not quite 1., because of floating point arithmetic:

In[12]:= 8.62097/8.62097 // InputForm

Out[12]//InputForm= 0.9999999999999999