In a series of tests I ran years ago for Modern Photography I came up with
8
lines per mm .


Arthur Kramer
344th BG 494th BS
England, France, Belgium, Holland, Germany
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Is that 8 lines or 8 line pairs per mm?

8 lines would be roughly equivalent to 200 dpi (8*25.4 mm/in)

8 line pairs would be roughly 400 dpi