Here I calculate what we expect for the RMS in Larry's q and u plots just posted this week. I find that he is getting errors about four times bigger than those expected from photon noise. A likely culprit is intra-cycle-pointing-drift. Lero's GIF of M82 that he just sent me shows that the peak flux is 15 Jy per 9 arcsec beam, and the size to the FWHM is about 18" by 45". This is Larry's "source". (Contours are 1, 3, and 10 Jy per beam, according to Lero.) Thus, Larry's source is 4 x 10 pixels, but since its not rectangular we expect it to be about 30 pixels. Since there are 30% dead pixels, we expect about 20 pixels which is about what Larry gets (he gets about 23 on average according to his memo). The average flux in Larry's source is somewhere between (15/2) Jy per beam and 15 Jy per beam. Lets use 10 Jy per beam. A 9" beam is 64 square arcsec, which is 3 SHARC-II camera pixels. So we have 3.3 Jy per camera pixel, on average, for Larry's source. This is 7 times the brightness required for 1% SHARP polarimetry in 5 hours, when binning pixels in 2x2 (see Table of Specification posted to instrument section of public SHARP web page). Thus we should be able to achieve 1% polarimetry in (5/49) hours = 6 minutes. However, since we are combining 20 pixels, not 4 pixels, this gets us to 1.2 minutes. However, for tau = 0.05 weather (and a x 25 multiplier to get to 350 micron tau), EL = 40 is 1.7 times lower transmission than EL = 60, so we should derate the sensitivity for this. Then we need 3.5 minutes to get 1% polarimetry. So in an 8 minute "cycle" we should be able to do 0.7% polarimetry. I took the standard deviation of the first 20 of Larry's values of q (they look better than most of the others), throwing out two outliers, and I get 3.0%. This is four times higher than what we should be doing based only on photon-noise errors. However, I am not too worried about this because there is another factor to consider which is the errors due to pointing drifts. According to my estimate on the web-logbook (Dec 3), these are 10% per cycle. By binning 20 pixels we reduce this a lot, but it would be surprising if we could achive the 0.6% per cycle expected from photon noise only. Still, this does mean that we have not yet proven that SHARP can achieve its sensitivity spec. For this I think we may have to analyze a fainter source than M82 where the photon noise per cycle should dominate the pointing-induced errors.