fiber.lm <- lm(strength ~ machine + diameter, data = fiber)
  rg <- ref.grid(fiber.lm, at = list(diameter = c(20, 24, 28)))
  rg
  
  # Note this is an emmGrid object defined in emmeans. The old "ref.grid"
  # class is now an extension of this:
  r.g. <- new("ref.grid", rg)
  lsmeans(r.g., "machine")
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