| Year | Annual |
| 1990 | 55.47 |
| 1993 | 74.905 |
| 1996 | 57.26 |
| 1999 | 57.76 |
| 2002 | 56.365 |
| 2005 | 50.9875 |
| 2008 | 47.595 |
| 2011 | 46.3925 |
| 2014 | 57.62909 |
| 2017 | 69.82409 |