A data frame with 81 observations on the following 3 variables.
Day
the day;
a factor with levels 1 up to 9
Mach
the machine used for measurement;
a factor with levels A, B or C
Perm
the permeability in seconds:
a numeric vector
Details
The data give the average permeability (in seconds)
of eight sheets of building materials,
using random samples of 81 sheets in three machines over nine days,
with three measurements for each machine--day combination.
References
A. Hald (1952)
Statistical theory with engineering applications.
New York: Wiley.