Strad,

I did the math and keep a copy in my bag


FILTER FACTOR & STOPS

FACTOR.. ..STOPS
1 0.0
1.5 0.6
2 1.0
2.5 1.3
3 1.6
3.5 1.8
4 2.0
4.5 2.2
5 2.3
5.5 2.5
6 2.6
6.5 2.7
7 2.8
7.5 2.9
8 3.0
8.5 3.1
9 3.2