In Table I we present a sample of our results for the coefficient
of static friction for three pairs of surfaces. We used a
smooth glass plane for the slip/tip measurements, and then
elevated one end of the plane with lab jacks for the measurement
based on Eq. (4) for the incline. Even though substantial
care was taken with the measurements, we do not obtain
complete agreement between the two methods for all of the
surface combinations, although most of the results are within
uncertainties. The disagreement for the Al block, even with
uncertainties, quite possibly reflects the limitations of the
crude model of Eq. (1) as well as surface inhomogeneities.