Nesting if statements

I am trying to nest 6 if statements, i want the statements to define the certain upper and lower boundaries to and to relate this to a letter
i have a total range of M31:M147 to apply this to but for this i am just gonna use M32. value of M32=2.37E-03
The rules i want to apply are:
A-<10E-6
B- >=10E-6 to <10E-4
C- >=10E-4 to <10E-3
D- >=10E-3 to <10E-2
E- >=10E-2 to <10E-1
F->=10E-1

the if statement i have written is:

=IF(M32<10E-6,"A",IF(10E-6<=M32<10E-4,"B",IF(10E-4<=M32<10E-3,"C",IF(10E-3<=M32<10E-2,"D",IF(10E-2<=M32<10E-1,"E",IF(M32>=10E-1,"F"))))))

but this wont come back with a letter, it always just comes back with "FALSE", not "D" as i would hope.

Thanks for the help.