Assumptions:

• Source density at J at high latitude is 632 sources per square degree, which are also observed at H. (This value is twice the K density at SNR = 10 in the coadd, and agrees with T. Jarrett's star count model for SNR = 10 at J and H.) Note that these stars are SNR 3 in the individual frames, used for the position reconstruction.

• Pixel sizes of 2 .

• Individual position determinations accurate to one sigma = 0.2 pixels.

• 6 degree long scans overlapped by 5/6 resulting in 260 frames. (Note that this is different from the 8 degree long survey scans, but the results should be quite similar. We will do 8 degree long scans next.)

• PPM stars picked randomly along the scan, used to obtain a simple offset only to tie the scan to the reference system. Results are categorized by the number of PPM stars found on a scan, from 1 star per scan to 7 stars per scan. The quoted accuracies of the PPM stars were simulated.