Year	mm per year
1961	1668
1962	1668
1963	1668
1964	1668
1965	1668
1966	1668
1967	1668
1968	1668
1969	1668
1970	1668
1971	1668
1972	1668
1973	1668
1974	1668
1975	1668
1976	1668
1977	1668
1978	1668
1979	1668
1980	1668
1981	1668
1982	1668
1983	1668
1984	1668
1985	1668
1986	1668
1987	1668
1988	1668
1989	1668
1990	1668
1991	1668
1992	1668
1993	1668
1994	1668
1995	1668
1996	1668
1997	1668
1998	1668
1999	1668
2000	1668
2001	1668
2002	1668
2003	1668
2004	1668
2005	1668
2006	1668
2007	1668
2008	1668
2009	1668
2010	1668
2011	1668
2012	1668
2013	1668
2014	1668
2015	1668
2016	1668
2017	1668
2018	1668
2019	1668
2020	1668