Dear Dave:
	Here are the average areal densities of the combined Cu and C
targets used in the second half of 2004.

rho-t Copper: 0.7987 ± 0.0016

rho-t Carbon: 0.671 ± 0.004

These errors correspond to 0.2% for Cu and 0.6% for C, the agreement
between Dave Meekins' result and these numbers was very good for Cu
(0.02%), but no so good for the C targets (0.6%).  Assignment of
these errors is not very rigorous, but more of an educated guess.
But I believe the errors on Dave's report are based on the accuracies of
his scale and the resolution of the toolmakes microscope, and thus too
small. If the edges of the foils are straight, then the error on the
average areal density is much better, but of course the beam does not
interact with the entire foil, hence one must factor in the
uniformity.  Generally, we use a micrometer, which gives us
confidence if measuring a hard target (not so great for gold).  There is
clearly a problem with the carbon target, since we assume that the
individual foil rho-t's should agree, but do not.  As seen in the
Jan05 carbon target, this indicates problems in the area
measurements (i.e., just measuring the coordinates of the corners is
not good enough.)

If you want the details, I can send you my MathCad worksheet, just let me
know.
	-Jim