#   ADU    Arp mpv  Arp CI
-   ---    -------  ------

8   25507  14.78    +0.60
9   35197  14.22    +0.90
31  64000  13.09    +1.11
64  64000  13.39    +1.03
65  10158  16.52    +0.60
66   8895  16.95    +0.51
67  11986  16.19    +0.51
68  12537  16.13    +0.52 
74  11868  16.00    -0.12
75  64000  12.87    +1.21
88   9100  17.1     +0.55
bkg 6500

Photographic measurements from 1955 with the 100-inch telescope
calibrated by photoelectric sequences. H. Arp, AJ 60, 317 (1955)

ADU from image m15_300_c.fit, slightly out of focus, taken on 25 September 2006.

Saturation approximately 14th magnitude at 64000 counts.  Sky approximately
6500 counts.  Faintest identified star is 17.1 at 2600 counts above sky.