Aldergek taught me this one
s1 = sensitivity you need
dpi1 = dpi you're going to use
dpi2 = dpi you're using
s2 = sensitivity you're using
dpi1 x s1 = dpi2 x s2
soooo using the skills i learned in the 6th grade, you substitute the values you have and leave the variable you dont alone
so, for example
1800 x s1 = 450 x 3.4
s1 = (450 x 3.4)/1800
s1 = 1530/1800
si = 0.85
okay i realize that isnt REALLY accurate, but i'm sure you can just adjust the values
I really don't get it because i am stupid as fuck