Filter factor?

Hi there, I'm new to this group.
I have been experimenting a bit with paper negs in a 9x12 folder I got just last week.
Now, I would like to try using some old Ilford "Filters for Multigrade Paper" (by simply holding them in front of the lens!)
There is three different filters: "low", "medium" & "high".
My question is; how should meter?
Would it make sense to hold the filter over the light meter as well?
Have you tried something like it?