Scans 109 through 116, inclusive, from the night of 970521 are the only group of May survey scans yet processed for which we have pre-defined survey tiles. For these eight scans the tile corner for the west edge closest to the equator was compared to the corresponding corner of the actual scan [to compare only the 6-scan-covered area, 414 (5 times the step-size of 82.8) arcseconds were excluded at each end of the scan as listed in the "4-corners" file]. The nominal tile declinations were defined as the tile declination listed in the tile database plus 6 step distances (82.8 arcseconds per step is the value used for May observations) toward the equator on one end and the file database declination plus 6deg poleward on the other end. Distances on the plots are in arcseconds, computed by subtracting the reconstructed position from the nominal tile position.

This first histogram shows that the actual 6-deep scans are placed approximately 24 to 34 arcseconds south of the tile's equator-most declination.

Tile declination at the edge farthest from the equator was calculated by adding 6 degrees to the declination given in the tile database for comparison to the corresponding scan declination. All of the scans fall within 2 arcseconds north and 13 arcseconds south of the nominal pole-ward tile edge, as shown in the second histogram, below:

The third histogram shows the right ascension in the tile database to vary from approximately 8 to 19 arcseconds east of the scan corner.

Many thanks to Eric Howard for clarifying the tile boundaries.