Is there really a difference between a 15.5 and 15.4 computer screen?

I think Monk might notice the difference, or he might just prefer the 15.5 to the 15.4, given a choice between the two, but that’s a measure of the diagonal of the screen so in terms of the relative height and width of the the two screens I just can’t imagine that any normal human could actually perceive a difference in the sizes.

You also have to factor in manufacturer’s dishonesty. It might be a 15.5 screen, but .1 of that may be covered by the bezel. I would go with @lillycoyote and say that even if the viewable portion was 15.5, that extra .1 probably won’t make a difference and should fit.