| The table below gives standard magnitudes measured through B, V, and I filters for the standard stars used to calibrate our images of M13. Each star is indicated by both a letter which corresponds to the markers in the above picture and its Stetson identification number. |
| ID | Stetson ID | B Magnitude | V Magnitude | I Magnitude |
| A | 566 | 14.021 | 12.899 | 11.68 |
| B | 572 | 14.497 | 13.514 | 12.410 |
| C | 518 | 14.427 | 13.433 | 12.324 |
| D | 1407 | 13.781 | 12.484 | 11.140 |
| E | 1465 | 15.187 | 14.356 | 13.357 |
| F | 1232 | 14.257 | 13.197 | 12.039 |