The depth correction of MBT by Ishii and Kimoto is given by
Coefficients of the time-varying MBT depth bias equation: d = Dz+Cz^2. Units of coefficients C and D are
10^-4 m/m2 and 10^-2 m/m, respectively. The coefficients before 1950 and after 1994 is the same as those for 1948 and
1996, respectively.
Co efficient C and D are provided in table below


Year   C      D 
1950  2.71  -0.57
1951  2.75  -0.66
1952  2.75  -0.66
1953  2.76  -0.68
1954  2.75  -0.66
1955  2.02  -0.16
1956  1.98  -0.11
1957  1.64   0.04 
1958  1.61  -0.01 
1959  1.87  -0.43 
1960  1.64   0.00 
1961  1.18   0.51 
1962  1.00   0.98 
1963  1.05   1.11 
1964  1.35   0.90 
1965  0.62   1.52 
1966  0.59   1.58 
1967  0.67   1.36 
1968  0.73   1.26 
1969  0.33   1.68 
1970  1.03   0.80 
1971  1.26   0.71 
1972  1.14   0.95 
1973  1.08   0.88 
1974  1.02   0.96 
1975  1.27   0.75
1976  1.64   0.54
1977  1.59   0.34
1978  2.96  -0.94
1979  2.30  -0.22
1980  2.80  -0.85
1981  2.86  -1.02
1982  2.61  -1.00
1983  2.15  -0.83
1984  2.79  -1.44
1985  2.22  -1.11
1986  1.82  -0.98
1987  1.84  -1.17
1988  2.02  -1.37
1989  2.00  -1.48
1990  2.16  -2.07
1991  1.72  -1.61
1992  1.75  -1.66
1993  1.74  -1.65
1994  1.56  -1.49