PEG ratio - use leading or trailing EPS?

CFA Level II
#1

I would think leading, correct? Or does it matter?

#2

that would have to tell us which one to use.

#3

leading.

#4

I just looked this up in schweser. They don’t explicitly say, but their example uses leading p/e. Which makes sense since this is projected.

#5

There is a question in the CFAI book from 2006 exam which asks which of the following has stocks has the lowest PEG ratio. But it does ask to find it using leading p/e.